Notes on the Type XXI

[Leandros]

Originally Posted by 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..

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.

Originally Posted by Marcello

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.

Originally Posted by Marcello

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.

Originally Posted by Marcello

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]

Originally Posted by Leandros

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, the 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 limited Germany to parity with Britain in submarines.

[Leandros]

Originally Posted by the dark knight

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, the 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 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]

Originally Posted by 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

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]

Originally Posted by BigWalleye

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

[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 , 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





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



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

[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)