Notes on the Type XXI

[Marcello]

I will use this thread to post informations and personal observations on this type of u-boat. I use GWX,Commander, Stiebler patch and Wreford Type XXI mod (http://www.subsim.com/radioroom/downloads.php?do=file&id=1357)(plus SH5 water mod and ASDIC MKI)

Speed settings I use
- Transit: 5 knots + surface runs at full speed in foggy/bad weather or when enemy air is relatively light.
- Transit in case of heavy enemy air presence: 4 knots
- Snorting and using the periscope: 3-4 knots
- When looking for targets in the patrol area: 1-2 knots
For reaching and leaving the patrol area I have come to the conclusion that in the game a speed of 5 knots is the best compromise between the various factors.Assuming 100% charged batteries at the start and a 15 minutes snorkel run to replenish air supply it will leave you with about a 70% charge at the end of the daily run; enough to deal with any emergency. Thereafter batteries can be topped again in three hours and half.
Only when I do not plan to engage anything along the way and enemy air is less pressing I will push to 6 knots.
On the surface I will usually run at full speed to minimize diving time, though in the safer areas I may run at standard speed.

In real life ther snorkel was often used at 5 knots, personally I find that the vibrations in the game at such speed are not worth it, however useless the periscope might be to detect aircrafts I still prefer to be able to look around. On the other hand going too slow is not practical as there will be depth keeping issues and you want to minimize snorkel/periscope exposure.

[Marcello]

Crew
AFAIK actual Type XXI crew was something like this

6 Officers Commander, 2 x Watch Officers, Chief engineer, Watch engineer and Physician.
4 Chief petty officers (Diesel, E-Maschinist, Obersteuermann and Funkmeister)
1 Boatswain,
14 Petty officers (2 seem., 8 techn., 2 funktechn. and 2 torpedotechn.)
33 Seamen (12 seem., 16 techn., 3 funktech. and 2 torpedotech.)

Personally however I prefer to cut down the seamen to 28 (10 seem., 14 techn., 2 funktech. and 2 torpedotech) and leave out the physician. This way everyone can be rotated between watch duty and rest or simply kept at rest until needed; in the latter case this means I always have a reserve of men always fresh. Otherwise number can be increased to nominal; the the medical officer however is still better left out as there are only two rest slots for officers and besides they were in short supply in real life.

[Marcello]

Snorkel
Personally I set the maximum permissible wind speed for snorkel use at 13-14 m/s, as it appears (http://www.uboatarchive.net/U-1229INT.htm)that employment at Force 6 might have been possible, if barely. I however limit its use at Force 5-6 to the strict necessary.
While I do not know how well the game handles the matter it is a good idea to keep a close eye to depth to minimize snorkel head exposure to radar. The "è" key (at least in the keyboard I use) will bring you to snorkel depth, slightly deeper than normal periscope depth, which will reduce the amount of manual adjustment necessary. Automatic depth keeping and hovering gear was supposedly fitted to at least some of the boats.

Leros, at least as far late war operations in hot areas are concerned, is a don't go out without item. Observation periscope should be left up for realism's sake but actual usefulness is limited, both in the game and real life.

[Marcello]

Fresh water and torpedo load
The Type XXI was fitted with the same water still of the Type IX. The plant however was not designed to be operated at snorkel depth and to do so would create all the sort of issues with piping, heat management and IIRC contamination of distillate by salt water during pressure drops caused by the snorkel valve shutting off. The XXI water needs, owing to the larger crew and more cells, were also greater than the IX; the XXI would thus have to rely largely on its water tanks. The postwar american reports note that at at US style consumption rates water would have lasted less than a couple of weeks. It could have been stretched further with conservation measures and, according to a source, by using trim tanks for extra storage but if you want to be realistic a prolonged stay in in tropical waters in 1944-1945 is probably not a good idea.
However, U-2511 destination before surrender was the Caribbean, whether the issue had yet to become apparent to BdU or it was deemed manageable for a short stay I cannot say.
The issue was fixable with a properly designed water still, whether the germans were working on that I have not been able to determine.

The XXI ws fitted with enough tubes and racks for 23 torpedoes, but three racks were left empty for moving and servicing the weapons.
There is a mod to simulate this that can be found in this thread (http://www.subsim.com/radioroom/showthread.php?t=202526). No list of the actual types carried is know but it can be inferred that TIII Lut II would make up much of the load, with perhaps a smaller proportion of passive homing torpedoes (TXI likely) than that carried by conventional U-boats. FAT torpedoes would not be carried (mechanical incompatibility or so I have been told).
Advanced torpedoes were in the pipeline, though of those only the T VII is partially modeled in the game.

[desirableroasted]

Thank you for your notes.

I note that you use Beaufort Scale for windspeed... are you calculating that yourself, or is there a mod out there that reports in Beaufort? Having lived right on the ocean some years, that is how I think about windspeed, and would love to have it in the game.

[Marcello]

I calculate it. No idea if there are any mods.

[Gustav Schiebert]

I usually calculate it as well but you can confirm by checking the windspeed from the Navigator's weather report. 1 m/s is about 2 kts, so the worst weather in game (15 m/s) is about 8 kts, which looks right to me.

[desirableroasted]

Yes, the navigator reports m/s, which is also how I think about wind after so long in Europe, but I just thought he stumbled across a Beaufort calculator.

http://en.wikipedia.org/wiki/Beaufort_scale

[Marcello]

Maximum diving depth
The XXI was designed with a theoretical crush depth of 330-340 meters, a design depth of 135m with a safety factor of 2.5. However structural issues, such as the way the bottom pressure hull was joined to upper one and workmanship problems meant that this could not be attained, joining two sections for example required a continuos weld taking about 8 hours to complete that could not be interrupted without creating weak spots
(not good news in 1944-1945 for reasons that will be obvious...) .
Some of these issues were being addressed, for example assembly was going to be moved in special bunkers, but nervethless various studies and estimates put the crush depth to as little as 245 meters or at most just past 300m.
Thus if you want to play realistically the depth gauge, limited at 260m, is pretty much spot on in terms of what you can get away with.
If you instead assume that somehow the design was properly debugged you have in the game at least another 50 meters to play with before taking damage.

[Marcello]

Stern watch station
Some drawings report it but as far I can see from the available pictures its existance is debatable.
http://img10.imageshack.us/img10/1548/rnka.png

[Marcello]

Battery charge
As far as I have been able to find under test condition it took about two hours and half to go from 10% to 60% (1st charging stage), another two hours and half to go from 60% to 90% (2nd charging stage ) and another two hours and half to achieve 100% (3rd charging stage). The third stage stage was used periodically to conserve battery life, in most cases the 2nd would be used. If you are interested in realism not fully regharging the batteries every time might be an interesting addition to gameplay.

[the dark knight]

Stern watch station
Some drawings report it but as far I can see from the available pictures its existance is debatable.
http://img10.imageshack.us/img10/1548/rnka.png


I would agree. I have never seen the stern watch station in pictures. Perhaps a few of the Type XXI's had them, but it seems like most did not.

[Marcello]

Alberich
As far I can tell, whatever plans might have existed to fit the XXI with Alberich coating were in the realms of wishful thinking. Rubber was a scarce material in wartime Germany and would have likely remained so under any circumstance (even in case of a victory against the USSR probably). As far I have been able to find out the priority, aside from the experimental vessels, was to use whatever could be produced for the Type XXIII and the Type XXVI. In practice only some of those would probably fitted with it and only a XXIII was actually equipped.

[Tupolev]

Was the planning to coat the entire hull with Alberich or just the mast heads of the scopes and Schnorkel?

Or am I thinking the radar coatings?

T

[Marcello]

The radar absorbing coating was applied ony to the snorkel head. Earlier in the war the possibility of applying such materials to the tower for surface operations had been investigated but it was quickly realized that the radar signature could not be reduced to a sufficient degree. Materials were either Buna (the synthetic rubber of Auschwitz fame) mixed with iron oxide powder or alternatively a somewhat more complex layered structure using carbon black, foam and paper/plastic. Not sure what combination of both was actually deployed.
Alberich was made up of Oppanol (again sysnthetic rubber) tiles with air cavities to absorb sound, both ASDIC pulses and the u-boat machinery. Naturally since the whole boat had to be protected from both the coverage had to be pretty much complete. This unlike the snorkel RAM meant a lot of material, carefully applied and probably rather maintenance intensive. A small, frequent turnaround boat such as the XXIII must have been somewhat more manageable.

[Tupolev]

Thanks for the info.

Good point with the short patrols on the XXIII. Makes me wonder if any progress was made on a better adhesive for the sonar coating from earlier attempts.

T

[Marcello]

As far it can be read, some progress was indeed made but the issue has probably not been really fully 100% solved yet, going by the pictures of modern boats with missing/flabby tiles.

[Marcello]

Radar
The Type XXI is fitted with FUMO-65.To be honest my experience is that it has been almost useless. I do not kwow if it is my mod soup to blame but I get an oscilloscope, not the most user friendly interface instead of the PPI it was supposed to have.
In terms of actual perfomances it seems to have never picked up anything that had not been already detected by visual or RWR except in the worst visibility conditions and even then it was non radiating targets, else the RWR would have probably picked them up first. Manual operation might yield better results but as noted the interface leaves a lot to be desired. It is also not clear what the range knob actually does in practice.
Basically it is of some use only in bad weather and likely only against surface targets at that.

[Marcello]

Employment
Late war procedures for employment of u-boats can be found at http://www.uboatarchive.net. I post the sections relevant to the game.

Current Order No: 1. Issued Nov. 1944.


(Procedure when underway and in operational areas).



I. The Schnorchel has to a considerable extent, escaped enemy air attack and with the simultaneous decrease in U-boat losses, has enabled them to operate again, in areas strongly defended by aircraft.

Principles for Proceeding. The task of the Commander is to take the boat to and from the area of operations without any great diversions, to avoid skirmishes with the enemy defence, to utilize however, every opportunity for attack.

Principles for the operational zone. In order to make full use of the possibilities offered by the Schnorkel, approach close to the enemy shipping near the coast. Only there, are successes to be obtained.

II. Procedure of boats when underway and when in the operational zone depends on the strength put up by the enemy air force. Commander U-boats differentiates between areas with a strong, medium and weak defence. If a Commander establishes another aircraft position in an area, as described under A - C, he can intensify or modify his tactics according to the change.

A. Strongly defended areas. Squares AN, AF, AE, AM, BF, CG, DJ, AL, BE of the eastern third, further a strip of nearly 100-200 nautical miles off North and South America, including the Caribbean.

Procedure: on principle proceed submerged when underway and when on operations, recharge when Schnorkelling (total submerged warfare). Recharge only above surface, only when Schnorkelling is not possible for technical reason.

Execution.

1. On setting out and returning when Schnorkelling.

a). For more detailed instruction concerning schnorkelling times, boat routine, making best of weather conditions, see Current Order No. 20.

b). Normal cruising depth above 50 meters (162.5 feet) - At routine times and when taking hydrophone effects at periscope depth. Good hydrophone conditions in no way exclude periscope observations while proceeding.

2. When setting out and returning while submerged with charging above surface. Only in cases of a faulty Schnorkel or when other reasons (e.g. a too strong current) make it necessary.

a). Charging to be carried out, in conditions unfavorable for air attack, that is, in general, by night. Favorable - moonless, very dark, haze, fog, storm.

b). If at night especially great air and radar activity are observed, charging can be carried out in the daytime, in fog, or in clear weather with good visibility and good Ack Ack conditions. In case of doubt the proceeding by night is more favorable, since, in the event of an attack, better opportunity is afforded for submerging and for shaking off the contact, moreover, a simultaneous attack from several aircraft is difficult.


c). During charging, complete Ack Ack readiness. Commander on the bridge. Keenest lookout. All armament ready and unmasked, so far as weather conditions allow. Gunner in layer position with shoulder-piece in position. In weather conditions which enable accurate surprise attacks, if necessary man only the twin barrelled gun, in order to be able to submerge more quickly when located.

d). Set up the available FUMB. If there is FUMO on board, warm up well before surfacing, and use as follows:- Immediately after surfacing a circular sweep with the FUMO, then only Radar observation with "Wanze" and/or "Borkum and Tunis". If airborne locator has been observed, in general, submerge. If charging is urgent, when detecting a locator, D/F with FUMB, search by FUMO, and continue to observe the enemy. Until picked up by FUMO, a longer period (up to 30 mins.) can elapse. If no enemy is detected, do not return too soon to FUMB. If the "Hohentwiel" set is in perfect order and the servicing crew well-experienced, the apparatus, in continuous search alone may be used, when underway as an air-raid siren.

e). Do not remain on the surface longer than the time required for charging, as this endangers the boat unnecessarily. Exceptions: In especially unfavorable flying conditions and if the FUMO is functioning perfectly.

III. Procedure in the operational zone.

A. Submerged on principle and only while schnorkelling. On breakdown of the Schnorkel, in general, return to base. In this case carry out charging as under 11.

B. Keep close to traffic focal points and to coast routes, for it is only there that interception of traffic can be guaranteed. Lying on the bottom and taking advantage of the density of water which renders it more difficult for the U-boats to be intercepted by hydrophone and radar, facilitate, according to the latest experiments, a successful U-boat operation even at a depth of well under 100 metres (325 feet).

C. Initiate all measures for daylight attack, since this is most favorable. Submerged night attack promises success only at full moon.

D. Go frequently to periscope depth, do not rely upon the hydrophone. By night and when there is traffic, go down to the bottom, to save batteries.

IV. General Rules for "total submerged warfare".

A. Avoid surfacing by astronomical reckoning as far as possible. According to experiments so far to hand, extremely exact determination of position is made possible by very accurate dead reckoning, by taking the current into consideration and by making full use of the sounding device, electrosone and radio-beacons. When close to our own, or to enemy coast, make full use of every means of determining a position by land.

B. [...]

C. Even when proceeding without incident under water and when on operations, it is necessary to reduce the consumption of air and current to the minimum, in order to shorten the charging time and to have sufficient battery capacity for the attack when contacting the enemy, and further, in case of pursuit, to be able to run on it long enough without being forced to Schnorkel and/or surface.

D. Especially when the Schnorkel is out of order the boat must continue to run submerged in order to evade the shadowing aircraft and to be as faras possible beyond the range of location of the point of submerging, when it surfaces. Therefore when below water, not more than slow speed ahead, both engines. Use only the most necessary consuming plant, economize on light and air, the E-condenser consumes much current. Trimming and pumping with the auxiliary bilge pump. Carry out night routine according to Current Order No. 2.

B. Areas with medium air defence.

Areas not specified under A). Atlantic - North of 15 degrees South, coastal strips 100-200 nautical miles off the African coast, fringes of the Indian Ocean, including islands.

Procedure: Submerged by day, above surface by night.

a). In the open Atlantic between 30 degrees North and 15 degrees South, in clear, cloudless weather, with good Ack Ack conditions and with the FUMO switched on, proceed on the surface; without the FUMO, on principle, submerged. FUMB locating has been intercepted, dive and remain for a while submerged. If the enemy holds you on his Radar beam, he later sends out carrier planes, operating from sight.

b). Above water keep Ack Ack gun ready for firing and by day at least six look-outs on the bridge.

C. Areas with weak air-defence.

Atlantic - South of 15 degrees South, open spaces of the Indian Ocean.

Procedure: On principle, on the surface, FUMB continually switched on.



Current Order No. 2


Procedure when Schnorkelling. Issued Nov. 1944.



Many undertakings of 40-60 days duration were carried out without surfacing. The Schnorkel proved very effective and through it operations were again possible in areas heavily patrolled from the air

a). In General.

? Principle: Under all circumstances attempt to recharge battery completely every day. On account of enemy positions the Schnorkel is not to be shifted. Continued reduction of the battery capacity can finally cause the boat to be in especially dangerous situation.

(1). Chose favorable conditions for Schnorkelling, i.e., in general at night, in a swell, poor visibility. By day only in clear weather with good visibility, the emotion of the sea from force 2 and is the Schnorkel does not smoke. Best at night, once 2-3 hours at the beginning and end of the night.

(2) The Schnorkel is not undetectable by radar. If the Schnorkel is correctly manipulated, that is to say, with the exhaust under water, it can be scarcely or only inaccurately intercepted. The motion of the sea reduces the possibility of being located. If the Schnorkel is fully raised, it can be located and attacked, therefore it is wrong to let the Schnorkel protrude too far when there is phosphorescence, so as to avoid a trail of foam. Then interception through location by radar is possible at a much greater distance and therefore more often than by a trail of foam. The range of location of the camouflaged Schnorkel is about 10% of the boat when on the surface. In practice it is scarcely interceptable.

3). Air attacks on dark nights are generally only possible with the use of artificial light. If a searchlight is detected shining directly on the boat or a flare above it, sound the Schnorkel alarm, and dive to at least 80 metres (260 feet). If searchlights and/or flares are detected searching a long way off, or their location is above the Schnorkel dipole, only sound the "quiet-Schnorkel-alarm", that is to say, dive to 20-30 metres (65-95 ft. approx).

4). When the Schnorkel is in use, periscope manned by the commander and officers of the watch in watches of roughly 1-2 hours. In boats of type VII C, turn the main periscope continually by hand. In boat type IXC in general, only the periscope for air observation. The raising of both periscopes results in oscillations, and moreover increases the danger of being located by radar. Do not proceed at too high a speed (i.e., with both Diesels on screw (aufSchraube)) this endangers the periscopes. They swing, bend and become leaky and cloudy; slight oscillations are frequently corrected by very small alterations of periscope height.

5). Noise caused by Schnorkelling is about the same as when the boat is running on both E-engines at a rate of 200 revolutions per minute. In areas where there is hydrophone activity do not refrain from using the Schnorkel because of the fear of being heard. According to experiments, boats have proceeded unperturbed with the Schnorkel in use, with hydrophone bearings of weak signal strength and with "circular saw noises" of medium signal strength. "Circular saws" on shadowing vessels cut out other noises.

6). Circular acoustic sweeps for enemy positions every 15-45 mins. - (unreadable) - dive to a depth of 20 metres. It is possible that

the shadowing craft makes towards a U-boat which it has intercepted by hydrophone and in order to remain undetected, will stop when the boat stops her Diesels in order to make a hydrophone sweep. Therefore measures have to be taken to be ready for a circular acoustic sweep as soon as Diesel engines are stopped.

Execution.

a). Order to engine room, central control and listening room: "Ready for circular acoustic sweep".

b). Switch off charging, charging diesel engine, electric fan and condenser.

c). Lighten the boat in order to avoid further pumping, once the Diesel engine has been switched off. [...]
d). Engine room telegraph to "Dive". Cruising Diesel is to be turned off and the E-engine run, utmost silence in the boat, and keep a listening watch.
e). [...]
f). [...].

Methods of Proceeding.

a). Schnorkel in sea up to force 6-7 (according to type of boat) steer broadside on, 1-5 degrees, with the ballast forward, with as little flooding as possible, otherwise current and air unnecessarily consumed when pumping prior to the circular acoustic sweep. Choice of cruising speed depends on the motion of the sea, and the oscillations and angle of the periscope.

b). Whenever possible ventilate the boat at least once during the day, for 15 mins. with the Schnorkel; this saves potash cartridges....


Personal comments
The XXI does regain a part of the mobility lost by the II/VII/IX forced to remain underwater, though it cannot really match the capabilities of surfaced submarines.In actual terms it is feasible to pursue most contacts detected by hydrophone and to expand the area of operations to the western approaches. Going to let's say America is going to be a somewhat time-consuming affair however and chasing ships moving away at medium/ fast speed is unfeasible/risky.Personally I patrol just off che continental shelf, where chances of mines is less, I can make full use of depth and traffic is still enough to be able to pick and choose what to engage.

Antiaircraft firepower il less compared to conventional u-boats, while diving time is pretty good, so staying on the surface during air attacks is less appealing than ever. In real life getting in and out the antiaircraft positions would also be somewhat awkward, while the rear one had a direct hatch access to the hull leaving the forward one would apparently entail climbing through the turret hatch and then back in the conn. Considering three people (one gunner and two loaders) and the fact that the early version could dive in as little as 20 seconds (eventually increased to improve underwater performance but still fast) and it does not look good. Personally I use my guns only when close to the harbor where I cannot dive.

[mikey117us]

I Research as much as I can when I have a Keen interest in a subject and on the Elektro-Boots of Type XXI and XXIII are an area I scoured books and the Internet for Data. ( I changed my Type XXIII to Reflect Reality based on the Royal Navies Secret Evaluation conducted in Scotland on Surrendered U-2326 ) I did not change the Type XXI to reflect what was built and the one boat that went on a war patrol sinking no ships but testing its remarkable stealth before its surrender to the Allies. The Royal Navy had been slated for their own type XXI for Evaluation but after the secret tests performed on the Type XXIII U-2326 they told the Russians and the Americans they did not even want it as they found no useful technology or performance variables to suit the needs of the Royal Navy. They Concluded the Schnorkel was at best a Desperate Measure for a Beaten Enemy and their Interest in a Walter Boat was Furthered. ( they eventually got Dr. Walter Himself hiding him from the Soviets and whisking him back to Britain to Aid them in developing Futuristic Propulsion Systems ) They Found: The Pressure on the Eardrums and Discomfort of the Men Detracted them from Performing their Duties to the Utmost. The Elektro-Boats are a "Wet" Boat Moisture Seeps Everywhere even more so than a Hull of Standard Shape. The Type XXIII was a simple Boat designed for a Single Purpose to divert attention from the Atlantic for 6 months and then Hit Hard with the Type XXI's on the Long Abanandoned Convoy Routes of The Western Atlantic.

Type XXI Boats With two 1970 H.P. MAN 6 cyl.
main engines (4 cycle, M6V40/46 with
(supercharger, at 520 RPM Max

Had to disengage the MAN Superchargers before Starting the Diesels for Underwater Propulsion with a Blocking Arrangement on the Exhaust Manifolds due to the Engines having a Higher Manifold Pressure then Specified by the Design. After The MAN Factory was Bombed Production of the SuperChargers Ceased for a time and Most Type XXI Boats went into Service without them reducing the surface speed at FF to 12-13 knots. Engines were mounted at Assembly Yards to the aft section and the SuperCharger was Installed Then and could not be Installed Later at all. ( The Majority of MAN Superchargers after Production Resumed were then sent to Yards Building Type IXD2 Boats )Halting Construction was out and as the Boats were designed to mostly stay submerged this was not deemed critical to its purpose. Radar was used as a Navigational Aid not as a Tactical Advantage in Practice. but in Theory one could in Weather not suited for Periscope or UZO Attack plot Torpedo Attacks for the LUT Pattern-Running Torpedos, however using Radar for this was Suicide. The Type XXI and XXIII could launch Torpedos from 20 meters Depth and by Sound and Sonar the type XXI could Plot Torpedo Attacks while Submerged without the Periscope into the side of a Convoy and Evade at Silent Speed Reload and Attack Again. This Stealth, quick Reload Time, and Fast Submerged Speeds was how the Germans were going to to Tip-the-Balance back to their Favor again with a New Atlantic Blockade. The Starvation of Britain, and the Allied Invasion Collapsing for Lack of Logistical Support and Great Britain and The United Staes would then Sue for Peace. This Link has Valuable Data for in Depth Study of the XXI as well as other valuable information found on the site.

http://www.uboatarchive.net/DesignStudiesTypeXXI.htm

[Marcello]

There was no way the elektroboot would be able to force the british and the americans to ask for terms. By 1943 the americans alone were turning out a million of tons of merchant ships per month and while given the commitments the shipping situations was not always rosy all the sort of measures would be implemented to prevent Britain from going under, including delaying offensives if it became necessary. The new boats were indeed tough nut to cracks but large numbers of frigates/DEs carrying Squid and the latest ASDICs were still a threat to them, the occasional detection of the snorkel from the air was still possible and so on.
In addition the new u-boats had to be built, sheltered and supported by at least a minimum of surface and air forces. The components factories were of course liable to fall under the increasing threat of Allied air power but even hardened facilities such as Valentin assembly bunker or the Keroman shelters could hold only so much against repeated Tallboy and Grand Slam attacks. Sperrbrecher were needed in numbers to prevent the allies from simply paving the harbours access routes with air dropped mines and to provide air defense to the U-boats at least until they could leave the shallower area; unlike the U-boats or the E-boats putting them under concrete was just not feasible and losses were heavy, about 50% of the force.
Without at least a chance of the Luftwaffe showing up the facilities could thus be pounded, eventually with some success, and allied air/naval forces forces could come closer and closer to blockade the bases.
What the XXI could accomplish was enabling the Kriegsmarine to resume the battle of the Atlantic, instead of the naval guerilla war they fought in 1943-1945 but that is all. Best case scenario they delay the end of the war by a few months so that Germany is nuked or a greater portion of it ends under the soviets. Not so great outcomes for them.

[Marcello]

As for the Type XXIII, it was essentially the elektroboot equivalent of the WW1 era UB I: small, railroad capable coastal boat built to operate in shallow areas. Unsurprinsingly they both ended up with a somewhat lacking armament (two bow tubes and no reloads) though of course the XXIII had an edge in speed/range. Had it been a mere stopgap instead of filling a different tactical niche they would probably have dropped the railroad requirement and specified at least a pair of reloads as for the Type XVII. The elektroboot/Walter equivalent of the Type VII never became ready of course.

As for the superchargers issue I do not know, Blair of course goes on rant about it as it can be expected but probably it is true that their specs were over ambitious and the lack of Diesel power might have some effects on charging times. In addition it is worth noting that U-2540 postwar had theirs replaced with a different type while the original electric motors and most others components not involved in tests were retained; it may have been simple convenience but perhaps there were real issues.

[Marcello]

Oxygen settings
According to the sources I have found it could take 27 hours for oxygen in the air to drop from 21% to 17% though this was probably calculated on the basis of reduced activity on the crew part.
A renewable oxygen supply setting of 2.5 and silent run (entailing reduced crew activity) seems to get fairly close to that result in the game. It should be noted however that under the same conditions as above chemical scrubbing of CO2 would be initiated after 11 hours,well before adding bottled oxygen became necessary and since the supply of of CO2 absorbing compound cartridges was large (enough for 19-23 days of operation) but not unlimited a brief daylight snorkel run is still advisable for realism sake when feasible.
Non renewable oxygen supply is bit harder to assess.Installed flasks capacity could apparently vary from boat to boat, 1200 liters (at 150 bar) could be typical but up to 1500 liters were also possible. In addition a number of IG-brikett, each capable of generating 1500 liters of oxygen, were also carried, 25 could be a typical amount.
Total oxygen stored for the 1200 liters flasks + 25 brikett configuration would thus work out at something about like 217500 liters (1200 x 150 + 25 x 1500) if my math is right.
Human oxygen consumption at rest is about 15-16 liters per hour, increasing up to four times that for light work and up to eight times for hard one, though probably most of the typical activities aboard a would fall under the former category.

EDIT
While I had previously suggested 2.0 for non renewable oxygen supply 1.5 seems to square better with available data. I still have to try out 1.0 just in case.

[Leandros]

Employment
Late war procedures for employment of u-boats can be found here (http://www.uboatarchive.net/BDUOrder1.htm) and here (http://www.uboatarchive.net/BDUOrder2.htm). I post the sections relevant to the game.

Current Order No: 1. Issued Nov. 1944.


(Procedure when underway and in operational areas).



Interesting info. Tks for posting.

Fred

[Eastwa]

What about battle tactics in 1944-45 with an XXI type sub.

Every time I go out in one I still get sunk even with the great underwater speed

[Leandros]

What about battle tactics in 1944-45 with an XXI type sub.

Every time I go out in one I still get sunk even with the great underwater speed
Do you ever get homing torpedoes in your weapon arsenal?

What I have found during the latter part of the war - if you try to evade going deep you shall rarely get out of it if there is a number of subhunters looking for you - regardless of your speed. Besides, using your speed shall always reveal your position to the hunters. They'll usually have better range than you so sooner or later you are stuck in the mud. If there is bad weather on the surface and you are lucky with your stealthy tactics you may make it.

The best is to sink the opposition from periscope depth when its coming against you (takes a certain technique and depends on the proficiency of your torpedo officer...:03:..). Self-seeking torps is the obvious choice for this. Talking real life I am not sure how the Germans reckoned this. To me it seems like a logical conclusion that this torpedo type and the XXI should be part of a weapons system. I know a ship's load of Zaunkønigs was on its way to Bergen in April '45 (I believe) but the freighter was sunk. If the XXI's received any before this I do not know.

For the game it should be no problem, the first types (Falke) are available from the last part of 1943.

Fred

[Marcello]

What about battle tactics in 1944-45 with an XXI type sub.

Every time I go out in one I still get sunk even with the great underwater speed

Personally I use the maximum speed only in short bursts to get out of a hedgehog or depth charge pattern.Trying to outrun a convoy escort will only result in collecting a pack of DE on your back, and while they seemingly cannot shoot you while you run it is not a competition you can win. IMHO the main selling point of the type is not the absolute maximum speed but the sustainable cruising speed and the relatively high silent speed. At 100 RPM you can do more than three knots and the game standard silent speed is over four.

Now, following the procedures listed in the operational orders I quoted, in particular "total submerged warfare" and using the snorkel mounted RWR it is possible to largely avoid air attacks except for the bombing raids at the beginning of the patrols. Possibly non radar equipped planes could still suprise you but it never happened to me.
I also give a wide berth to task forces and I do not troll lone destroyers; in addition I treat all the continental shelf near Britain as a potential minefield and I stick to deep waters as much as possible.
In general in my favorite hunting areas off Britain most of the traffic consists of two ships groups sans escorts and while it is usually small fishes you can still bag a decent amount of tonnage with the XXI torpedo load. Against convoys what has worked for me is the diagonal approach at periscope depth and at quiet speed, getting inside the convoy, fire a salvo, go deep (always at quiet speed) and turn towards the rear of the convoy and trying to dodge the rear escorts as they run over me. I cannot however say that, unlike in dodging air attacks, I have enough experience in this area to be authoritative.

[Leandros]

What about battle tactics in 1944-45 with an XXI type sub.

Every time I go out in one I still get sunk even with the great underwater speed
There is another item which can help. The little I have played with the XXI it seems to stand damage better than the other boat types. In that respect it helps a lot to have a good repairs crew - and to have them in place before action. After torpedo personnel I prioritize the repair crew. If you get hurt - remember to turn off the "silent" mode. And back when repairs have been made. I have got out of some pretty bad-looking situations by not giving up on repairs. Give priority to flooding control. Don't lay still. If they are pinging you it is only a question of time.

Fred

[Leandros]

As the tactical situation developed in 1943/44 it is natural to see the XXI and the home-seeking torpedo as a weapons system. For the German submarine force the emphasis had turned to one of pure survival rather than being the hunter.

To that purpose this combination was a good answer, if too little, too late. I would like to underline that to influence the war, as it developed, this weapons system would have had to come into service as early as mid-1942, as a dedicated escort-killer from the start - just my opinion. If it could have taken a high toll on the Allied escorts, with the conventional U-boats consequently reaping better results with the merchant fleets, the whole convoy system could have been brought out of balance. However, to achieve such a result the project would have had to be put into gear before the war started. The technology was there. But to achieve this, purely industrially, something else would have to give. What comes to mind is the dropping of the Kriegsmarine's larger units - Graf Zeppelin, Tirpitz and Bismarck. Or a slowed-down development of the German army.

Marcello has made some good postings on RL restrictions in the use of the XXI and its systems, mainly the schnorkel and periscopes related to cruising speeds. To that comes the state of the German homing torpedoes in 1944. They had developed a lot since the year before with higher speeds, better seeker-equipment and combined impact/magnetic pistols. The last versions are also said to better be able to outsmart the Foxer.

A word on their alleged efficiency, or lack thereof. At first they were believed by the Germans to be quite effective. After a while Dønitz became suspicious. Problem was, the tactical doctrine was such that the boats should dive after firing the torpedoes to avoid being hit by "friendly fire" - torpedoes turning back on them. Therefore, the results could not be verified even if detonations were heard. While this may be correct it may also be wrong. First of all, the Allies, and particularly the British, were quite good at hiding there losses at the time. Secondly, the vessels may well have been hit, and deactivated, but not being sunk. This is not so strange as torpedo hits would probably be in the aft part of the ship. The propulsion and steering gear could be destroyed but not necessary the floating capability. With other words, not reported as sunk, but with a much lessened capability of fulfilling its mission - to defend the convoy. The "hit" could also have been on a Foxer device. If so, that Foxer would have been destroyed and the escort in question would be vulnerable to another homer, but let off the hook as the sender had dived. That said, the Foxers were in themselves a hindrance to the escort's mission. It reduced its speed and shelved the sonar emissions of the enemy U-boats'.

Right or wrong, in the game you can, with correct tactics, stay up. If SH is anything like RL, or if we can make it such, I have developed a tactic which works quite well. First of all, I use a conventional torpedo as often as I can to save the homers. For no other reason than you usually do not get enough of it. In the game you can get six or more, depending on how you play the game.

So, start out with as large a load-up of homers as possible. A little note - the XXI has no rear tubes - that can be a disadvantage. Start out with at least 2 homers in the tubes. This is less sensitive than in a conventional U-boat as reloading only takes about 2 minutes. But see to that you have a good torpedo crew that can make use of this functionality. Switch off the automatic reloading function. You want to load up with another homer when you have used one. Always use magnetic, one meter below the target. In 1944 the torpedoes had started to run true.

Important: Decide early which targets you find worthy of a homer. It needs to stand out from other vessels so that the torp is not deviated. Fire the torp early, distance 1.000-2.000 meters if the target is approaching you. Use manual aiming. Observe the target's advance and aim along a mean line between you and the enemy vessel. If possible, remove yourself along that line so that he follows you and cross the path of the torpedo. You can also lay still and make yourself known by showing your scope at maximum height. If you are not intending to run position yourself on an approx. 45 degree angle on his approach and prepare a deflection shot with a conventional torpedo (TI). After that you need to go full ahead and dive to 40 m. - (use Bold) while turning towards him. Start immediately going up to periscope depth when you have passed under him.

If there is a second one arriving at the same time send one against both before you start running. They will follow you - and the torps will follow them!

The latest homers (TXI..?..) could be fired from a depth of down to 50 meters. This is a nice feature! I have not tried that deep in the game but if you have your scopes destroyed this could be your last chance to get away. Fire towards their sonar signature. Remember to aim a little ahead of it as the reporting is usually a little delayed. Use manual aiming.

Fred

[Marcello]

There were a number of reasons why the Kriegsmarine built the fleet it did in the 30's. Political constraints meant that a few capital ships could be built without triggering too many adverse british reactions, while on the other hand a large submarine fleet might not be tolerated to the same extent. A submarine required, ton for ton, a much greater quantity of copper/lead/rubber than a battleship and imports had to be economized even before the war; needless to say an elektroboot required an even greater amount of those materials. The capture of the Biscay ports could not be relied upon and without those the prospects of a proper tonnage war are dubious; in the event at least a minimum of a surface force turned out to be handy for the norwegian campaign.

[Leandros]

There were a number of reasons why the Kriegsmarine built the fleet it did in the 30's. Political constraints meant that a few capital ships could be built without triggering too many adverse british reactions, while on the other hand a large submarine fleet might not be tolerated to the same extent..
Actually, there were less restrictions on submarine building than surface vessels. They built as many surface vessels they were allowed (untill 1935 when restrictions became much more lenient) but not as many submarines as they were allowed.
A submarine required, ton for ton, a much greater quantity of copper/lead/rubber than a battleship and imports had to be economized even before the war; needless to say an elektroboot required an even greater amount of those materials..
Certainly, there would have to be a weighing between quantity and quality. The U-boats the Germans constructed, and built, before the war were, in principle, little different from those in WW1. That said, I am hard-up to believe that any 30.000 tons surface vessel would require less of anything than a 1.000 ton submarine.
The capture of the Biscay ports could not be relied upon and without those the prospects of a proper tonnage war are dubious..
Which is why they probably should have gone for quality rather than quantity.
in the event at least a minimum of a surface force turned out to be handy for the norwegian campaign.
The Scandinavian campaign was not decided on untill early 1940.

Fred

[Marcello]

Actually, there were less restrictions on submarine building than surface vessels. They built as many surface vessels they were allowed (untill 1935 when restrictions became much more lenient) but not as many submarines as they were allowed.Submarines were forbidden under the Treaty of Versailles and limited to a proportion of the british/commonwealth fleet under the 1935 terms. From what I recall they had indeed trouble fillling their quota (overall priorities and squabbling over which types should be built) but what they were allowed was in the event a far cry from the critical mass necessary to fight the global tonnage war Donitz envisioned.
He wanted 300 submarines and that, according to what Blair reports, was probably still just the bare minimum,perhaps insufficient. It is dubious that a decisive move in that direction would be politically and economically feasible given all the others necessary expenses.

That said, I am hard-up to believe that any 30.000 tons surface vessel would require less of anything than a 1.000 ton submarine.What I meant is that 30.000 tons of surface warships will require less of certain expensive materials that 30.000 tons of submarines. Obviously a single u-boat of 1000 tons will be less expensive than a battleship of 30.000. It will also have less impact.


Which is why they probably should have gone for quality rather than quantity.The issue is not quality but requirements. As long as the environment was permissive enough it was a lot better to remain on the surface: a WW2 era u-boat sailing on the surface with its diesel engines has greater mobility than a boat optimized for underwater perfomance and usually better situational awareness than what could be obtained from GHG and periscopes. So while in truth radar and the increasing importance of air power should have made clear that the surface night torpedo attack so much cherished by Donitz had a fast approaching expire date and the future trend would be towards underwater operation almost nobody was looking that forward. The japanese had a prototype elektroboot in 1938 capable of making 21 knots submerged but they did not order production types until 1943 under pressure from allied ASW. The italian navy had a workable snorkel developed in the interwar period, never installed.Did the british and the americans do something? Nothing deployed during the war I recall. In short abandoning the surface was usually only done under duress.
Also, needless to say, with the Luftwaffe seldom doing a good job one needed large numbers of boats for spotting

The Scandinavian campaign was not decided on untill early 1940.True but planning in the 30's one had to consider that such contingencies might arise. Placing all your eggs in a single basket while it is far from clear that such basket is a safe bet is a very risky move.

[the dark knight]

Actually, there were less restrictions on submarine building than surface vessels. They built as many surface vessels they were allowed (untill 1935 when restrictions became much more lenient) but not as many submarines as they were allowed.


As the poster above me pointed out, U-boats of any kind were strictly forbidden. At the end of World War I, as part of the Paris Peace Conference, 1919 (http://en.wikipedia.org/wiki/Paris_Peace_Conference,_1919), the Treaty of Versailles (http://en.wikipedia.org/wiki/Treaty_of_Versailles) restricted the total tonnage of the German surface fleet. The treaty also restricted the independent tonnage of ships and forbade the construction of submarines. However, a submarine design office was set up in the Netherlands and a torpedo research program was started in Sweden. Before the start of World War II, Germany started building U-boats and Submarines for other nations. Some of these project boats were meant for other countries, like the Turkish U A (which was a stepping stone boat from the Type Ia and was the fore-runner to the IXa) but the Germans kept the submarines for long periods of time claiming training and sea trials were being done. When this became known, the Anglo-German Naval Agreement (http://en.wikipedia.org/wiki/Anglo-German_Naval_Agreement) limited Germany to parity with Britain in submarines.

[Leandros]

As the poster above me pointed out, U-boats of any kind were strictly forbidden. At the end of World War I, as part of the Paris Peace Conference, 1919 (http://en.wikipedia.org/wiki/Paris_Peace_Conference,_1919), the Treaty of Versailles (http://en.wikipedia.org/wiki/Treaty_of_Versailles) restricted the total tonnage of the German surface fleet.
Sorry, bad wording by me. Regarding the U-boats, what I meant to say was that practical restrictions were lifted in 1935.

Regds

Fred

[Marcello]

To that purpose this combination was a good answer, if too little, too late. I would like to underline that to influence the war, as it developed, this weapons system would have had to come into service as early as mid-1942, as a dedicated escort-killer from the start - just my opinion.

The TXI would have been neutralized as the TIV and TV were. A purely passive homer, and with 40's technology at that, had just too many drawbacks to remain competitive for long past the initial surprise. There are good reasons while wire guidance and active sonar have been incorporated. Wire guidance was being tested by the war's end and something like "Lerche" (a passive homer that could be manually steered from the u-boat) might have seen service.

[Eastwa]

Actually made a successful patrol in a XXI in 1945, submerged all the time, sank 60000 Grt, and attacked a heavily escorted convoy with success, three ships sunk plus two damaged. I was detected by the escorts but I went super deep to 260 metres and escaped quiet easily, I'd always been afraid to go to those depths before in the XXI but obviously the boat can handle those depths.

Regards
Eastwa

[Marcello]

A collection of technical articles (http://translate.google.it/translate?hl=it&sl=es&tl=en&u=http%3A%2F%2Fwww.u-historia.com%2Fuhistoria%2Ftecnico%2Farticulos%2F2 1tecnico%2F21tecnico.htm) about the Type XXI, regarding issues such as construction, layout, antiaircraft armament, sensors, planned variants (ranging from cargo carriers to convoy killers fitted with 18 torpedo tubes) etc.

[BigWalleye]

Actually made a successful patrol in a XXI in 1945, submerged all the time, sank 60000 Grt, and attacked a heavily escorted convoy with success, three ships sunk plus two damaged. I was detected by the escorts but I went super deep to 260 metres and escaped quiet easily, I'd always been afraid to go to those depths before in the XXI but obviously the boat can handle those depths.

Regards
Eastwa

The performance capabilities of the computer model called "XXI" in what is generally recognized as a very flawed and frequently inaccurate simulation game should not be taken as an indication of the actual performance of a real physical Typ XXI submarine. The only extant example of the Typ XXI, Wilhelm Bauer (U-2540), has not been operational since 1982. For actual performance data regarding the Typ XXI, it is best to rely on published reports.

[Marcello]

The performance capabilities of the computer model called "XXI" in what is generally recognized as a very flawed and frequently inaccurate simulation game should not be taken as an indication of the actual performance of a real physical Typ XXI submarine. The only extant example of the Typ XXI, Wilhelm Bauer (U-2540), has not been operational since 1982. For actual performance data regarding the Typ XXI, it is best to rely on published reports.


260 meters with an actual production XXI would be flirting with death, though perhaps barely possible. The game allows you to push to 300 and beyond, which was the theoretical crush depth. Going by memory there were issues with either the lower pressure hull or the way it was joined with the upper one that created a weakness but whether it was something that could be easily rectified or that required a total redesign I have no idea, the type was something of a work in progress even in May 1945.
Off hand I also vaguely recall that the antiradar coating would be damaged beyond a certain depth perhaps 120-140 meters, but pinch of salts need to apply.

[CCIP]

Just wanted to thank you for this fantastic thread. I've never played Type XXI before because it seemed ahistorical and I saw its modeling in the game as really simplified and overpowered, but the information here will be of great help to develop house rules and play out a realistic, immersive XXI experience :yep:

[Marcello]

Since it is of interest I have done some cleanup in the thread, consolidating and updating some of the previous posts with new info.


Type XXI tactics could not be ironed out during the war for obvious reasons. Neverthless Erich Topp wrote a manual for the type on the basis of available information, a copy of which can be found here (http://www.u552.de/german/docs/TypXXI/TypXXI.htm) , unfortunately I do not believe a translation from german is available on the web.

Tactical consideration are made in some books, primarily from the allied perspective.
The Royal Navy and Anti-Submarine Warfare, 1917-49 Malcolm Llewellyn-Jones


http://s24.postimg.org/6rz4hnolx/tactical.jpg
http://s8.postimg.org/ga4su2zb9/tactcal_2.jpg

In regards to how the actual attack could be carried out:

http://s1.postimg.org/dtsi6301r/Type_XXI_tactics.png

As a matter of fact the plans for the adoption of Schnee Organ in almost all subsequent designs would suggest that the germans came to doubt that firing multiple salvos was in fact feasible. It should also be noted that in real life the emphasis was placed on saturating a convoy with pattern-running torpedoes.

Also

The U-Boat War in the Atlantic: Volume III: 1944-1945 Bob Carruthers

http://s12.postimg.org/8fnamiou5/packs.png

[Marcello]

The issue is not quality but requirements. As long as the environment was permissive enough it was a lot better to remain on the surface: a WW2 era u-boat sailing on the surface with its diesel engines has greater mobility than a boat optimized for underwater perfomance and usually better situational awareness than what could be obtained from GHG and periscopes. So while in truth radar and the increasing importance of air power should have made clear that the surface night torpedo attack so much cherished by Donitz had a fast approaching expire date and the future trend would be towards underwater operation almost nobody was looking that forward. The japanese had a prototype elektroboot in 1938 capable of making 21 knots submerged but they did not order production types until 1943 under pressure from allied ASW. The italian navy had a workable snorkel developed in the interwar period, never installed.Did the british and the americans do something? Nothing deployed during the war I recall. In short abandoning the surface was usually only done under duress. On further thought the point deserves some additional food for thought to clear some misconceptions. Building an attack submarine optimized for underwater performances was not a new idea, at the end of WW1 the Royal Navy did exactly that.
http://en.wikipedia.org/wiki/British_R-class_submarine
Granted there were problems in the execution however they still built something that was at least a quarter of a century ahead of any other existing submarine. Yet the trade offs were simply not worth it for most submarine missions in that era and it is significant that some were in fact modified to improve surface performance.

[Marcello]

Some fighting instruction from BdU, for those interested in the late war environment.


Current Order No. 4 - of December 1944.

When assigning an area of operations, the High Command does not always have sufficient material concerning the focal points, routes and times of traffic. At times it can only give general outlines to the boats. Therefore, it happens that boats, in spite of remaining for long periods in operational areas assigned to them off the enemy coast, have not found the traffic suspected there by High Command and/or very little traffic or traffic proceeding by night and have not made contact or achieved any successes. In such cases it is absolutely necessary that the commander, after careful consideration and impartial estimation of the situation in the area of operations, frees himself from the existing ties after an adequate period of deliberation and fulfils his main duty of sinking ships; he follows where his flare and hunter's instinct sense possibilities of success. If no prospects of success exist in the original area of operation, he may seek out another area. For example to run closer to the coast, to penetrate deeper into the bays, and thus occupy the apparently more difficult areas. A report to High Command from the operational area, about a decision, is not required. All deliberations and actions, which are undertaken through responsibility, aggressive spirit, drive and the absolute desire for annihilating the enemy, will at any time receive the approval by the High Command.

[Marcello]

Current Order No. 67 - Issued November 1944
Firing torpedoes on the basis of firing data obtained by sound-detector
I. The captain can gain the best idea of the tactical situation by visual means. The periscope is therefore the most reliable instrument for observation. The captain should try to obtain his firing data by means of the periscope.
II. Under present wartime conditions however, U-boats may find themselves in a situation where use of a periscope is impossible. It is then a question of making the best use of the situation, if possible for firing purposes. This is all the easier if the U-boat is equipped with sound-detector apparatus and search gear. Captain, who, are solely dependent, however, on the sound detector must be clear on the following possibilities of attack
a) U-boats can be in such a position that individual ships or convoys are passing overhead before they have had the opportunity of using their periscopes. In this case it is considered possible to make a rough estimate of the general course, speed and range, using sound-detector and stop watch only. The use of a "Zaunkönig" torpedo or a Lut-fan for attacking from astern, will, in such cases, have certain prospects of success
Special attention must be paid to the following:
1) The firing of torpedoes is up till now only possible from a submerged depth of 22 metres. Therefore endeavours should be made to fire from a depth of 20 metres [...]
2) As soon as it is suspected that a ship will pass overhead, an attempt should be made as soon as possible to estimate speed and general course in order that only slight alterations will be necessary when the ship is actually overhead
3)Stop engines when the ship is directly overhead and continue checking the range referring to the estimated speeds until the moment of firing
4)Prompt decision must be made by the Captain, which type of torpedo is to be employed (Lut of Zaunkönig)
5)Directly after firing, the U-boat must dive to a greater depth (at least 50 metres), in order to avoid the possibility if torpedoes passing overhead, when traveling to a higher level. (When firing Zaunkönig torpedoes, speed should not exceed 3 knots)
6)Rapid grasp of the situation and speedy manipulation of the firing control apparatus and torpedo tube is absolutely necessary
b) If a ship does not pass directly above a U-boat, the firing data obtained by sound detector alone, are generally not sufficient to ensure the successful use of torpedoes
The Captain is not in a position to judge by sound detector alone his position and range in relation to an individual ship or convoy. It is not sufficient to know the enemy's speed only when firing a torpedo. In spite of these inadequate particulars if the Captain has the impression that the situation is favorable, he should fire, if he foresees no further opportunities of attack during the operation, or for example when leaving the area of operation or when returning to base

[Marcello]

Current Orders No. 24 of March 1944.

Prowling in greater depth - Experiments have proved that the revolutions for prowling at periscope depth can be increased at greater depths without increasing the possibility of the boat being intercepted, that is, at a diving depth of 20m. 25, 30m. 40, 40m. 55, 50m. 60, 60m. 65 more revolutions than for prowling at periscope depth. (Increasing to more than 70 revolutions for prowling even at greater depths, is not practical)

Further experiments have proved that when proceeding submerged then noise of one U-boat screw is more strikingly audible over a great distance than when both screws are running. When being chased for purposes of acoustic interception, therefore, avoid running on one shaft only as far as possible.

When proceeding at great depth, a hydrophone watch is to be kept for the noise of the screw. If the noise of a screw is picked up, its revolutions per minute must be reduced, until the noise disappears. When prowling the number of revolutions is to be selected in such a way that no propeller noises are registered in the multi-unit hydrophone. The limit of increase to 70 revolutions per minute prowling is made because of the booming which commences with any further increase. (According to experience, commences at approx. 180 revolutions per minute)

[Marcello]

Current Order No. 63 of November 43

Procedure for T V torpedoes

1) The increasingly strong defence of the enemy, compels us to take full advantage and make a success of every opportunity of firing which occurs, even when take by surprise. The TV is the weapon, qualified to make the U-boat the dangerous attacker and not the hunted, even in the case of clashes with the enemy.

Since in the Iceland channel up to 20° West and in the Bay of Biscay to 2° West, anti-submarine surface patrols are mainly to be reckoned with, cruises through the maritime area are to be made with as many T 5's as possible in the tubes.

2) At night carry continually one bow and one stern tube, with T 5 if possible, ready to fire. That is to say: flood tubes, bow cap open.

[...]

3) With unexpected targets, one should fire over the netcutter with positions between 20-160° ahead over the cam.

N.B. In case our own U-boats should be operating in the same area, it must be remembered that firing is forbidden against U-boats unless definitely identified as the enemy.

[Marcello]

Current Order No. 64 of October 1944

Procedure for firing Lut torpedoes in unexpected combat

Emergency setting T IIIa - Lut I
1) The current order no. 6 contains instructions for immediate firing of a turning torpedo (without director angle computer) in unexpected combat
2) On the sudden approach of destroyers, after firing a "Zaunkönig (Wren) torpedo in defence, naval operation T IIIa Lut I offers the further possibility of the use of torpedoes.
3) Emergency setting T IIIa - Lut I -
Loop: Short, V - Lut (TorpedoFitting): 11 nautical miles
Track 180, Preliminary run: 500
Firing angle: 0 or 180, Gyro-spindle: engaged
Depth 4 meters, Tubes: secured
4) With this fine adjustment, immediate torpedo track can be launched against the enemy, only, however, in position 0 to 5 degrees - and with enemy speed 15 at distance of 1000 to 2000 metres and 20 at 1000 to 3000 metres. Parallax should not be considered.
5) In other positions or with greater distances "Lut" firing procedure should be followed (Firing with a director angle computer)
[...]
7) In firing "Lut" torpedoes, tube No. II primarily, in the 4-fan tube mounting (if not set for firing turning-torpedoes) secondly tube No. III, should be used, in order to have available the 3-fans I, II, and IV or the 2-fans I and IV (with V-Lut and deviation on preliminary firing)
[...]
9) The recommendation in Current Order No. 42 that "Lut" torpedoes should should be used in cases where the enemy is suspected of using anti-T V defence, in the form of immediate readiness of T V and "Lut", i.e. if occasion arises, the tube loaded with a "Lut" torpedo should be open and ready for firing, instead of the tube loaded with TV

[Marcello]

Type XXI trials footage

U-2513 using the snorkel

https://www.youtube.com/watch?v=SobV1yIY7t0

U-2513 in a crash dive

https://www.youtube.com/watch?v=QY2jOqFZCmI