Decks awash: A scam?

[IonicRipper]

I was reading this article... Here's what they said about decks awash:

"If the center of gravity and the center of buoyancy are coincident and if a wave were to hit the boat from the side, capsizing could occur. Those Hollywood movies where a submarine is shown with decks awash, making an approach on the surface is mostly fiction. That is about where the two centers become coincident and it doesn't take much to roll the boat over."

Apparently (according to this article) they never used decks awash in WWII.
Can someone confirm? (Or refute.)

The article in question: http://www.subvetpaul.com/Flt_Class_Sub.html

[Cybermat47]

I'm not sure if the U-boat aces had decks awash, or just stayed on the surface. And is the article talking about USN Fleet Boats and U-Boats?

[Sailor Steve]

They're talking strictly about US boats, but the problems would be about the same either way.

I know that night surface attacks were common, but I have no clue about decks awash. It will be interesting to see what comes out of this.

[troopie]

I've read the same thing elsewhere from a (now forgotten) different source. I believe it, but can't get my head around the physics of it; surely the boat would be more top heavy the higher it is out of the water? Personally though, I never use decks awash; feels like a cheat to me. Surely the increased drag travling that way would've been undesirable? Also, I'm unsure If any in-game advantage is gained, I mean, do other units register that you're sitting a little lower in the water, or simply that you're surfaced?

[Sailor Steve]

...surely the boat would be more top heavy the higher it is out of the water?
When the tanks are empty the major weight involved is the keel, which is designed to keep the ship upright. With the ballast tanks full the boat now has more than 350 tons of water on board, most of it in outboard tanks level with the boat's normal waterline. Once submerged the center of gravity is balanced, but surfaced it looks like any serious ocean motion could possibly be catastrophic. I don't know if that's true or not, but now that I think about it I see how it could be possible.
http://www.maritime.org/fleetsub/chap4.htm

Personally though, I never use decks awash; feels like a cheat to me. Surely the increased drag travling that way would've been undesirable?
Running all over the ocean with no penalty is certainly a cheat, since the game allows it to work when in real life fuel consumption would rise dramatically. The main idea would be to use it only to lower the profile in a night surfaced attack, and to facilitate diving quickly in the same situation. Also the game assumes you're surfaced, and since you have no control over which engines you use you are automatically running on diesels, when part of the point in a surfaced attack is not to be heard as well as not being seen you would certainly be running on batteries in that situation.

Also, I'm unsure If any in-game advantage is gained, I mean, do other units register that you're sitting a little lower in the water, or simply that you're surfaced?
I don't know that one either.

[Claves_Mortis]

Also, I'm unsure If any in-game advantage is gained, I mean, do other units register that you're sitting a little lower in the water, or simply that you're surfaced?

For every surface attack I will go to a depth deep enough to just allows me to get on the bridge / UZO. I am doing this because obviously everything "on top" of a wave / the water is affected more by the waters movement than everything "inside" the wave / water is, meaning that if you are as deep as possible (while still being able to use the UZO) you can use the advantage of the x7 magnification while reducing the shaking part caused by waves, being able to do more precise usage of the UZO.

I do not know if that is historicaly correct, but in Silent Hunter 4 it does work (for the more steady view). If you do live at the sea you can easily try that yourself: get into a small, light (somewhere around 2-3 meters in length will be a size where you can easily realize it) without any equipment and only yourself in it - shaky. If you get your outbord motor, your gas tank, anchor, chord, some friends and maybe some water in your boat, resulting in lying deeper in the water the waves won't shake the boat as much anymore and the boat will also be less affected of your movement (leaning from left to right for example), it will still move, but slower and more predictable.

I also have no idea if it affects the ability of how easily the submarine is spotted by other ships in the game, but as how far your periscope does stick out of the water does affect the chance of being spotted (I am pretty sure about that, but it's only what I feel / experience, no written prove for that), I could imagine how far the tower is above the water does count too.

[IonicRipper]

I remember conducting a surface attack on a lone merchant on a fairly clear night with decks awash at approximately 1200 yards. My first shots missed (i think i miscalculated the torpedo depth) but he never spotted me or the torps so it gave me a chance to recalculate and ultimately, skin him. I should have saved the game and try the same thing fully surfaced to see if would have spotted me. I might try that with the mission editor some time today. I'll keep you guys updated.

[Bilge_Rat]

That is certainly an interesting question and one which has puzzled me for a long time.

Running "Decks Awash" in the sense of having the decks underwater with only the Conning Tower above water does not appear to have been used in attacks. Blair's three books on ww2 sub warfare does not mention an attack with "decks awash" (i.e. decks underwater). The Official manuals, i.e. the 1943 German sub commander's handbook and the 1946 U.S. Fleet submarine manual also do not discuss this attack tactic.

Without delving into the difficulty of maintaining a sub level in the open ocean with decks underwater, there would also appear to be little tactical advantage. A submarine is already hard to spot. The hull which is only a few feet above water is very hard to spot. The Conning Tower is also hard to spot from the lookout station/deck of a typical freighter since it usually is below the horizon. There would not appear to have been a big advantage in concealment in running with decks under water.

There also seems to be a confusion as to what "Decks Awash" means. Some submarine which were recorded as "running decks awash" had their decks above water, but had some seawater already in their ballast tanks so they could dive more rapidly. Their decks would be above water, but lower in the water than normal. For example:

http://upload.wikimedia.org/wikipedia/commons/e/ee/HMS_B11_Under_way_decks_awash.JPG

HMS B11 running "decks awash".

http://en.wikipedia.org/wiki/File:HMS_B11_Under_way_decks_awash.JPG

I suspect most submarines which recorded in their logs that they were running "decks awash" actually had their decks above water.

[Randomizer]

My (admittedly limited) understanding of this is that the author may be correct in general he is probably wrong about the particulars. He seems to be talking about the effects of metacentric height (GM), essentially the vertical difference between Centre of Gravity (CG) and the Metacentre which is related to the interior volume of the vessel. Centre of Buoyancy (CB) will be below CG in a stable floating vessel. High values for GM generally mean stability in roll.

The author seems to imply that when a submarine is running decks-awash, the CG=CB and therefore roll stability is lost. But since the boat retains positive buoyancy, this is impossible as the interior and the unflooded surface areas of the ballast tanks remain free of water. The boat may be more sensitive to roll but sufficient reserve buoyancy and a positive GM should exist to prevent capsizing.

I recall that both Prien mentioned running decks awash in Scapa and Kretchmer used the technique in night surface attacks when conditions were favourable. It was common to flood down when loading external torpedoes into the boat as well, a difficult evolution in any sort of seaway.

Paul Schratz in Submarine Commander mentions his captain flooding down his Fleet Boat to facilitate rescuing pilots while life-guarding but I don't recall him mentioning the prevailing sea state.

For more on ship stability and metacentric height see:

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

http://www.gwpda.org/naval/gmdefn.htm

http://www.navweaps.com/index_tech/tech-009.htm

[Bilge_Rat]

I rechecked this morning, but in Blair's U-boat book, vol.1, Prien stated that he was on the surface when he went into Scapa Flow, no mention of "decks awash".

You can find many photos of subs with flooded decks when they were in a static state in calm water, i.e.:

http://www.history.navy.mil/photos/images/h69000/h69033.jpg

http://www.history.navy.mil/photos/sh-usn/usnsh-s/ss105.htm


USS Chivo moored with decks awash:

http://www.navsource.org/archives/08/0834117.jpg

http://www.navsource.org/archives/08/08341.htm.

[Randomizer]

I rechecked this morning, but in Blair's U-boat book, vol.1, Prien stated that he was on the surface when he went into Scapa Flow, no mention of "decks awash".
Gerald Snyder in The Royal Oak Disaster mentions Prien flooding down some to increase the effectiveness of U-47's rudders when entering Scapa (pg 87). Without context as to "normal" trim, it's impossible to know how deep this might have been or whether the decks approached being "awash".

This was the passage that I imperfectly recalled in my post.

Still, it demonstrates that trimming down the boat had uses and whether negative trim brought the decks awash or not is probably based on the specific situation and captaincy decision logic.

[Webster]

you also have to take into account the dive plans and forward motion anchor the stability of the boat so it wont want to tip over.

its just like the fishing boats that use outrigger planes to make them stable and not wobble around out there


as to running decks awash it was purely used to present less of a target in a situation where they would be spotted or come under fire so the idea is to get the best underwater speed you can by keeping the tower out of the water yet keep the stealth of being "mostly" out of sight.

i think it was a tactic that was rarely used and only under the right weather conditions

[IonicRipper]

I made a quick single mission to test if the game AI would see a difference with and without decks awash.

Fully surfaced, the enemy ship spotted my sub at around 2400 yards.
With decks awash they spotted my sub at around 1400 yards.

So the game does simulate this, which is a nice touch.

[Armistead]

As far as US boats, the term was used by some to define running heavy ballast, but mostly it was a term used in diving to denote decks were awash as the sub headed down.

I know I've read a few reports of Skippers running heavy ballast and remarking it lowered their profile some, course, they just wanted to get under quickly if needed.

In game, it does seem to have some effect on the height of enemy radar detection, but also depends on what mods you use. It does impact visuals as well if you dive deep enough where only you can man the bridge, but the reason is simple, if you're men aren't on the bridge with you, the game sees your sub as dived, electric engines on,..you're now a sonar target, but your scope can be spotted.

[AVGWarhawk]

I do not see anywhere in this thread conversation on the batteries as ballast. The batteries were as big as Volkswagen Beetles. There was fore and aft batteries. It would take quite a bit to roll the sub.

[BigWalleye]

Both Fluckey and O'Kane wrote about using "decks awash." IIRC, Fluckey went in to drop off the train raiders with "decks awash" to facilitate launching the rubber boats. He also reported running "decks awash" for an extended period when searching for survivors from the POW ship, to make it easier to pull men out of the water. O'Kane reported running "decks awash" when on lifeguard duty for a similar reason. Fluckey's POW rescues were notably in fairly heavy seas, too. If these two gentlemen say they could run a Fleet boat with decks awash and not turn turtle, I tend to believe them. Of course, there can be endless shades of meaning to "decks awash", so we can't easily compare what Fluckey or O'Kane did to the analysis at http://www.subvetpaul.com/Flt_Class_Sub.html. There is also a matter of degree between "decks awash" and "radar depth" and Fleet boats regularly used the latter. Check Fluckey, O'Kane, Beach, and Galantin for examples.

My personal best guess (and just my opinion) is that there is a point at which the analysis is correct, but that the R/L boats stayed as far away from that point as they could while still achieving as much of the desired effect as they could. Sailing around the ocean with decks awash does not reflect R/L practice, but using it tactically might.

[AVGWarhawk]

ANALYSIS OF ANTI-SUBMARINE ACTION BY AIRCRAFT

[ASW-6 No. 8]

Unit: VC-9.
Location of Attack – Latitude 50-40 N.
Longitude 35-21 W.
Date: May 22, 1943.
Time: 1704 (Zone plus 1).

1. The airplane was flying at an altitude of 1500 feet, enroute to develop a DF contact which the ship had obtained on a 59 group message transmitted by the submarine about 40 minutes previously. The weather was clear with broken cumulus clouds whose bases were at 1200 to 1500 feet, and with 15 miles visibility. Radar was not being used, and advantage was being taken of the cloud cover then available. Slight contact was obtained on the submarine running with decks awash at a range of 5 miles and somewhat forward of the starboard beam. This contact was obtained 7 minutes after the plane took off. Taking good advantage of the cloud cover, the pilot was able to launch his attack and drop his bombs before the submarine became aware of his presence. At an altitude of 100 feet, airspeed 175 knots, target angle 1500, the pilot released four Mark 17 flat nosed bombs with fuses set to function at 25 feet, and through intervalometer set for 80 feet spacing. The explosions were observed to straddle the submarine somewhat forward of the stern, with the explosion farthest forward occurring approximately abeam of and to port of its forward gun. Shortly thereafter the submarine submerged slowly but at an apparently normal angle of dive and left no indications of damage behind it on the surface. The pilot marked the spot with smoke bombs and circiled at 500 feet until relieved by another plane of the squadron about 20 minutes later. When he arrived over the carrier about 30 minutes after the attack, the pilot heard a radio report from the relief plane stating that he had attacked the submarine, which had by that time returned to the surface. He returned to the scene and assisted the other plane in strafing the submarine in an attempt to keep its crew from scuttling the ship after surrendering. This action took place approximately 25 miles on the convoy’s port quarter.

2. The entire procedure surrounding this attack, beginning with the interception of the submarine’s radio message, was excellent in every detail. The report of the action was complete and well prepared and was accompanied by a fine series of gun-camera photographs and enlargements. One of the enlargements is among the most unusual ever seen. Not only is it a good picture of an enemy submarine running with decks awash, but it shows two of the bombs still in flight. One of the bombs appears to have lost its flat nose and, apparently, some of its tail. Directly over this bomb is an unidentified, irregular-shaped object which may indicate that the bomb had struck the deck of the submarine while in flight. The other bomb appears quite intact and just about to hit the water almost at the submarine’s side.


http://www.uboatarchive.net/U-569-8-Analysis.htm

[SkyBaron]

Just recently read this from the USS Tautog seventh war patrol report, May 23, 1943 pg 9:

"Sighted enemy bearing 300°T, radar range 6600 yards. Enemy on course 210°. Too dark for periscope attack. Commenced surface approach, flooded down, decks awash."

Maybe Hollywood took inspiration from the Tautog. :)

[troopie]

Awesome conversation.

What I'm getting from it so far is that D.A.:

May have provided an occasional opportunistic tactical advantage.

Most likely was not common practice while conducting an attack.

Was probably often used as a trim/maneuvering tactic as needed, and, I imagine, keeping a sub level in varying sea-states/weather-conditions/mission-objectives/ballast/load-levels/states-of-repair/damage-conditions etc. would've been a constant trim operation with many needs for much variation.

Can be advantageous in-game (nice work IonicRipper), though unless used with a historical bias is really just an exploit.

What say you all?

@Bilge Rat: love your Avitar mate! Staunch, grumpy, alcoholic; I should have Captain Haddock as my Av. :haha:

[TorpX]

Yes. It is very interesting.

When I expressed doubts about this tactic a year ago, I was nearly accused of blasphemy. :)

I still have my doubts about it. I mean were they really "decks awash" or just "riding the vents".

In the cited patrol report of Tautog, did they wish to make a periscope approach, but fell back on a "decks awash" one only because they could not use the periscope? I really don't see how having the boat a few feet lower changes the stealth factor very much. On the other hand, I believe it would reduce one's speed substantially. This seems a poor trade-off to me.

I don't recall O'Kane using the "decks awash" tactic for surface attacks, or saying anything about any such thing making the boat harder to spot. He did however talk about the advantage of having the fairwater of the tower cut down. This seems like it would be much more significant. Does anyone know if this is replicated in the game?

[Bilge_Rat]

The official U.S. Navy Fleet Type Submarine manual contains basically the same info as the article the OP linked to.

To summarize, a surfaced submarine with dry tanks or a submerged submarine with flooded tanks is stable.

In between, a submarine with partially flooded tanks will reach a point where its "center of buoyancy" and "center of gravity" will coincide. At that point it is unstable and could potentially capsize. When a sub is diving or surfacing that point is passed quickly, so it is not a practical issue, but it could be dangerous in a "Decks Awash" situation:

http://www.maritime.org/fleetsub/img/fig5-07.jpg


At A, the vessel is floating with all water excluded from the tank surrounding the chamber. The center of gravity is at G and the center of buoyancy, B, is found by intersecting diagonals of the displacement.

At B, water has been admitted to the lower section of the tank. Using the diagonals as before, it is seen that the center of buoyancy, B, is now coincident with G and the unit is unstable.

At C, the surrounding tank is flooded and the unit is submerged. The center of buoyancy is at B2, the intersection of the diagonals of the displaced water. The unit is stable, the center of buoyancy and the center of gravity are in the same vertical line. Any rotational movement about the center of buoyancy B2 immediately sets up a restoring moment arm



full discussion here at pp. 55-61:

http://www.maritime.org/fleetsub/chap5.htm#5B

In addition, when you look at the operation of the tanks during a dive, you can see the difficulty in maintaining a stable "Decks Awash" situation:


The weight taken on is water, and it is flooded into tanks. The air, of course, is vented off the tanks as the water flows in. First, the large tanks, known as main ballast tanks, are flooded. These tanks hold 359 tons of sea water. (See Section 4A2.) The submarine now displaces 2,109 tons and draws approximately 22 feet of water. The main deck is not awash, since there are approximately 2 feet from waterline to deck. The ship still has plenty of positive buoyancy. Since the bow buoyancy tank vent has been open during this operation, allowing this free-flooding tank to take on ballast as the ship submerges, it is necessary to add to the displacement the weight of water taken on by the bow buoyancy tank (which belongs to the special ballast tank group).

This gives a new total displacement of 2,141 tons (2,109 tons plus 32 tons).

Simultaneously with the flooding of bow buoyancy, the safety tank also in the special ballast tank group, is flooded. This tank holds 23 tons of water, giving a total displacement of 2,173 tons and a draft of 24 feet. The decks are just awash, and some positive buoyancy is still retained, although the submarine is approaching a condition of neutral buoyancy. Two things remain yet to be done: 1) to take on additional weight, and 2) to distribute this weight so that fore-and-aft athwartship balance is maintained. This additional weight is added to the variable ballast tanks and distributed throughout the variable tanks by the trim system. With the ship in this condition, approximately 55 tons of water must be added to the variable tanks to submerge to a depth where the periscope shears are even with the waterline. The ship is not in a state of neutral buoyancy and is balanced both fore-and-aft and athwartship. At this point, any additional ballast taken on will cause the submarine to submerge; any ballast removed will cause it to rise (Figure 4-1).



http://www.maritime.org/fleetsub/chap4.htm#4B

To summarize, to get the sub to a "Decks Awash" state in a dive, the main ballast tanks, bow buoyancy tank and safety tanks are flooded. However, the bow buoyancy tank is located in the bow and causes the sub to become nose heavy to make a dive easier. To maintain level "Decks Awash", the bow tank would have to remain dry and certain other of the variable ballast tanks flooded so that the sub is balanced both along its fore and aft and side to side axis. It is certainly theoretically possible, but would appear difficult to do in anything other than calm waters.

Again, I suspect that when a skipper wanted to lower the sub's silhouette, he would just flood the main ballast tanks which would bring the deck down from 10 feet to 2+ feet above the waterline. In the open ocean, that would usually result in waves breaking over the deck so the decks are "awash".




@Bilge Rat: love your Avitar mate! Staunch, grumpy, alcoholic; I should have Captain Haddock as my Av. :haha:

It seemed the right persona for THIS forum....:ping:

[Bilge_Rat]

waking up this old thread since I still don't have a clear answer on what is "Decks Awash".


I found photos of U-569 during the attack AVG posted about above (post #17). The Allied pilots had reported the sub was running "Decks Awash". That would have been a bit before the bottom picture was taken which shows the sub diving (no crew on deck) and 2 DCs dropped by the aircraft to the right of the photo.


You can see the deck was still flush with the level of the sea which would seem to indicate that the deck was a bit above sea level when it was running "Decks Awash".





http://www.uboatarchive.net/U-569DBs.jpg

[Admiral Halsey]

Personally I never run decks awash as I can normally get close to merchants at night fully surfaced.

[Aktungbby]

It seemed the right persona for THIS forum....:ping:
DAMNATION! I think yer on to something here!:Kaleun_Salivating: I only use decks awash to facilitate a swifter dive against any and all unforeseen opponents, especially after the skyblue color change of ASW aircraft to sky blue which shortened the the U-Boot con lookouts warning time considerably- Black MAY. I do miss the 'pitter-patter' of crew's feet when crash dive is ordered (SHII) into the bows to increase bow-plane 'bite' in the maneuver.:hmm2:

[merc4ulfate]

http://www.uboatarchive.net/U-569-8-Analysis.htm

[TorpX]

waking up this old thread since I still don't have a clear answer on what is "Decks Awash".


It is hard to pin down, isn't it.



I have always been skeptical that "Decks Awash" could be taken literally. I can believe that a sub with 8 ft. of freeboard might be flooded down to 4 ft. or even 2 ft., but it seems to me there would be problems with trying to cut it close.

Even setting aside questions of stability and the danger of capsizing, what is the main advantage of making a surface approach?

speed (clearly the biggest advantage)
better sighting?

"Decks Awash" can only reduce speed, and will not improve the sighting. It is thought that the submarine is much less visible, but it is not clear to me that this is so. Even if one is actually moving with the waterline at your deck, your tower is as visible as before, and you would have waves continually breaking over your deck so that it would be somewhat visible, to say nothing of your wake. I suppose you could sit still bobbing in the water, but without the ability to move, this is a very poor trade off.

[Harmsway!]

...and you would have waves continually breaking over your deck so that it would be somewhat visible

Your point is a good one. I make an effort to get into position long time in advance in order to cut my engines in a surface attack. I believe it is easier to see the water breaking than it is to see the subs hull.

I like to add this point to whether decks awash was used as an approach tactic. Any type of approach would have been practiced and drilled to perfection if it was ever to be consider in the bag of tricks. Do we have evidence of that being the case?

[Sailor Steve]

"Decks Awash" can only reduce speed, and will not improve the sighting. It is thought that the submarine is much less visible, but it is not clear to me that this is so.
The only advantage I can see to "decks awash" is an improved dive time if you're spotted. Since you're already at least partially flooded the boat will get down quicker, but I don't see that big a difference between 45 seconds and 30 seconds, so I've never seen a point to it. You also aren't going to cruise in that condition, because fuel consumption is going to go up quite a bit.

[TorpX]

The only advantage I can see to "decks awash" is an improved dive time if you're spotted.
I should have listed that, however, when I read "decks awash", I generally assume that they mean something more than just "riding the vents", but perhaps I shouldn't. Hard to really say without specific information. And, as you say, the difference between 45 and 30 sec. seems rather small.





Any type of approach would have been practiced and drilled to perfection if it was ever to be consider in the bag of tricks. Do we have evidence of that being the case?

That's a good point. USN submarine attack doctrine doesn't seem to mention it.

I just skimmed the U-boat commanders handbook at hnsa.org, and there is nothing about "decks awash" there either. Note that the main danger of being sighted, is considered to be that of having the conning tower sticking up above the horizon, or being silhouetted against the moon/moonbeam. It's hard to see how flooding down 5 or 6 feet helps much in this regard. I guess it would make you harder to hit, if you are spotted, though.



I. Danger of Being Sighted.
199.) As a matter of principle, the submarine commander should bear in mind that the submarine is always more difficult to see at night than any surface ship, unless the conditions of light are exceptionally unfavorable. The reliance of the commander on the invisibility of his boat at night increase with each new experience. Every contrary feeling must be overcome by the consideration that the enemy whom the submarine is attacking, being on the defensive, is in a weaker position, more especially as his lookout, in consequence of land gruelling periods of duty, is in no position to keep as good a watch as the submarine, which, at the moment, is concentrating all its energy and attention on the development of the attack.

200.) The difficulty of detecting the submarine at night on the surface due to its long and low silhouette, since it disappears almost entirely in the water, even including the conning tower. The conning tower can be most easily detected by the enemy, when it rises above the dip of the horizon, from the line of sight of the enemy. This is the danger zone for the approaching submarine. Against the background of the sea alone, the conning tower is very difficult to make out.

201.) The conning tower of the submarine always appears as a darker object, both in the dip of the horizon and against the background of the sea, and even on the darkest night. In our latitudes, the most suitable color for the conning tower, according to the experiences gained, is a light grey or a dull white-grey; in the Atlantic, a dark blue-grey.

202.) In view of the fact that paint, especially on the wet submarine, is liable to reflect the light (shine), care must be taken not to show the enemy the moon-lit side. If the circumstances make this unavoidable, the tapering silhouette should be turned toward him as soon as possible.

203.) Take care that the submarine does not appear in the track of the moon on the water; i.e., in the line between the moon and the target.

204.) Favorable conditions of attack, enabling the submarine to remain unseen:

a) Attack the enemy when he can be seen against the light horizon, or against the moon, and move toward him from the direction of the dark horizon, or the dark portion of the sea. In this case, the submarine itself is invisible even at the shortest distances from the enemy.

b) Go in with the sea, from windward, in order to reduce the head sea, which may well attract attention, especially if the sea is calm. For the same reason it is advisable to proceed at low speed when close to the enemy. This will also have the effect of reducing the stern sea, which is apt to betray the submarine if the water is smooth. In addition, the windward side has the advantage that it renders observation more difficult for the enemy, more particularly in a strong wind, or during rain.

c) During the attack it is always necessary and correct, to approach the enemy, up to the point of discharging the torpedo; i.e., of turning to fire the torpedo, in such a way as to show him the narrow outline of the submarine. The head sea and the stern sea then merge into one, and the form of the body of the boat itself, which might betray itself by contours of foam if it presented a larger surface to the enemy, is then sure to be invisible. A favorable method of attack is therefore to keep the submarine in the narrow position, and keep on turning, to show only the narrow outline of the submarine the approach by the "dog course" ("Hundekurve").
d) Caution should be observed during the transition from night to day, on account of the rapid alteration of the range of vision.

[Armistead]

The only advantage I can see to "decks awash" is an improved dive time if you're spotted. Since you're already at least partially flooded the boat will get down quicker, but I don't see that big a difference between 45 seconds and 30 seconds, so I've never seen a point to it. You also aren't going to cruise in that condition, because fuel consumption is going to go up quite a bit.

Realistically, I agree. I can it more running heavy ballast, not really decks awash, maybe 22 feet as not to effect speed, but get me down faster.

If you use one of the radar fixes in game, running decks awash may keep you under the radar.

[Bilge_Rat]

two questions I saw are:

1. what is "Decks Awash"? In game, you can run at flank speed with the decks completely under water and just the conning tower showing. However, it seems that was impossible in RL as discussed above. "Decks awash" seems to be having the MBT flooded so the deck level is lowered, but still above water.

2. As to when it was used, the advantage would be making the hull and tower harder to spot and lowering diving time. As a tradeoff, speed is lowered making it harder to escape on the surface. This is modeled in game, if you order a depth of 25 feet which basically brings the deck to just above water, flank speed is cut from 21 to 13 knots.

In RL, I could see two situations where "Decks awash" would be used. Either a night surface attack or as in U-569's case above, in daylight where there are a lot of aircraft around.

[Armistead]

Decks awash certainly cuts speed down in my set up. If I use it, I don't go as deep to cut the engines off and my crew is on stations. I know many go deep enough that the electrics cut on, but technically the sub is dived, just you can man the bridge yourself.

Seems my speed at flank is about 11 kts.