Type XXI evolution pondering

[stephenf555]

(APOLOGIES, REALIZED THERE IS A THREAD FOR THESE HISTORIC-TYPE QUESTIONS. COULD A MODERATOR REMOVE THIS THANKS.)

Hi folks,
Reading an encyclopedic book on the uboots at the moment. I was reading about the Type XXI, which seems like the first sub to be designed similarly to today's modern subs.

It struck me that it was kind of weird that it took until this point (1943?) to design a sub with a hydrodynamically efficient exterior. I would assume that any naval engineer worth his spanner would know that all the protrusions and flooding outer hull would greatly affect underwater speed. I know that the earlier subs were designed to spend most of their time on the surface and to be able to submerge for attack etc, but it still amazes me that they were covered in so much equipment.

So, I guess I'm wondering is why it took so long for them to design a hydrodynamic sub? Was it an engine issue...that only then did they get appropriate electric motors and batteries capable of spending longer times under water? Or was it that the deck guns etc were becoming redundant later on in the war? Or was it simply that one day they noticed that is they got rid of all the extraneous stuff the boat would be much more efficient underwater...though as I said, I assume they knew this long before?

[Sailor Steve]

Originally Posted by stephenf555

So, I guess I'm wondering is why it took so long for them to design a hydrodynamic sub? Was it an engine issue...that only then did they get appropriate electric motors and batteries capable of spending longer times under water?

I can't say for certain, but I would bet that you have the answer right there. Prior to that time the so-called submarine was considered more of a submersible - a surface ship that could attack from underwater. The hull itself had to be shaped for effecient surface travel, and submerged performance was considered secondary until proper propulsion could be divised.

Also, the "historical" thread is more aimed at US boats, as that is the OP's area of expertise. While I'm tempted to point out the dedicated Atlantic U-boat forum for SH4, you're fine with it right here.

Until the advent of radar and airborne ASW aircraft there was no requirement for submarines to operate exclusively submerged. Since they were submersibles rather than true submarines the hull shapes needed to be optimized for surface running. The limited target acquisition means available meant that in order to hunt effectively they had to do so on the surface.

The British R-Class boats of 1917 were the first submarines designed for ASW and had a fairly modern hull form with powerful electric motors and were capable of over 14 kts submerged.

A starting point for further info here:

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

So the basic technology for high-speed underwater performance existed early in the history of the submarine even if the sciences of hydrodynamics and acoustics were in their infancy, what was lacking was the need. Aircraft and radar doomed surface operations creating the military requirement for both high submerged speed and autonomous guided torpedoes but it was not until 1943 that these factors became important in the Atlantic and they were never decisive in the Pacific.

[Elektroniikka-Asentaja]

I may be in wrong thread with this thing but I remember reading from somewhere that some early U-Boat classes had problems with the pressure(?) hull, when they dived and the diesel engines were on the engines sucked the air from the exterior where the seamen were and therefore created huge pressure differences in the boat which caused "slight" ear damage to submariners..

I probably just wandered hell off the topic..

[Platapus]

If the induction (main air intake for the engines) was closed or other wise blocked or if a Submarine was equipped with a snorkel and it was blocked.

The engines would keep on operating and would take their air from the submarine, which being sealed, would lower the pressure causing great discomfort or injury to the crew.

[CCIP]

Yes, hydrodynamics were well understood and in fact the very early subs, such as the early Holland types, were quite hydrodynamic. There were also motors powerful enough even in WWI to achieve some quick speeds.

The issue, as noted, was one of doctrine and efficiency rather than technology. Surface performance and submerged performance are necessarily tradeoffs. An early hydrodynamic sub, which would've been small, would essentially be a sort of 'trap' restricted to a very short operating radius and inefficient at traveling any distance on the surface. To get around that issue, like the XXI, it would need to be very large, expensive and complex, while still sacrificing surface performance. Why do that when you have the technology to build subs that are smaller, faster on the surface, and have excellent sailing range, for just a small fraction of that cost? At the end of the day, a submarine's job is to sink ships without being detected, and escape without being sunk. It also needs to be able to return to port quickly, be prepared for the next patrol quickly, and get to its patrol area and sink ships again. A complex sub which compromised surface performance may be great at sinking ships and escaping, but in absence of fatal danger on the surface, it was a waste of time, money and energy getting it to and from patrol, and getting it in and out of base quickly. A sub fleet's function is to sink as many ships as possible, not as impressively but as efficient as possible - especially to the WWI/II mindset, tonnage war was not a psychological campaign but a very cynical game of numbers. The one who can outsink the enemy's production capacity wins. So it was a natural thing that navies operating submarines were looking for submarines that were the best compromise of all factors except overall fleet efficiency. What emerged, especially in the case of Doenitz's U-boat force (which was from the beginning was to be a commerce warfare unit first and foremost), is the ideal weapon for that time and those circumstances. It was a submarine that could efficiently go to sea, fight, survive and come back - and maybe it didn't fight as impressively as it could've, but in the circumstances and in the view of the doctrine, it was good enough to work to a devastating strategic effect. Unfortunately (for the U-boats) those circumstances changed quicker than the subs.

It's just like today, the idea of a supersonic transport aircraft is neither novel nor impossible. The Concorde has come and gone. But the fact is that there's no incentive to introduce another transport like that when what we have on hand are much cheaper, more reliable, and arguably still very fast subsonic airliners. The situation with subs was much the same, until technological change and vastly effective countermeasures forced the germans' hand and made them do their darnest to give the XXI all the performance they could, while investing a lot of effort into making its production faster and more efficient. But it was still too late.

[Rockin Robbins]

The United States could have designed submarines to operate more efficiently underwater. After all, the World War I S-Boats were very good underwater and actually were faster there than the fleet boats by a knot. However, the Navy was very interested in sinking more enemy vessels and very uninterested in features which had no payoff, like underwater speed and extreme depth capability. A submarine underwater at great depth is a harmless thing indeed.

The fleet submarine was designed wrong. It was assumed that subs would travel with the fleet and act as pickets, much in the way destroyers are used. That was lunacy, but it almost accidentally ended up with the best configuration for a diesel/electric submarine: a surface raider that can submerge for short periods of time when absolutely necessary.

There are several reasons why operating on the surface for the vast majority of the time was appropriate for diesel/electric subs.

First, the number of contacts you develop is directly proportional to the number of square miles of ocean surface you can search each day. If you are to remain submerged during search operations you can travel at a speed of about one knot all day. On the surface, traveling at best fuel economy, you would be traveling at 9 knots, a nine times increase in track length. Then your search radius improves, especially with radar. Eugene Fluckey calculated that without accounting for radar, based on high periscope search only he could search about 100 times more ocean area on the surface than he could submerged. That may not result in 100 times more contacts, but can you see that the comparison is just crazy good for the surfaced sub?

Second, a sub has to surface to charge batteries. A sub submerged all day surfaces with low batteries, maybe 25% charge left at best, and then spends the entire night with the lousiest possible fuel economy running the engines wide freakin' open not to propel the sub, but just to recharge the batteries. And the sub is not ready for combat during that procedure, having inadequate charge to attack and evade any contacts developed. The sub is at a critical disadvantage, lacking speed and endurance it may need to survive.

Third, for battling planes situational awareness is your friend. Playing ostrich below the surface, there is no way to detect planes overhead. But they certainly can detect you by wake and by direct vision. You will detect them by dying suddenly without notice. On the surface your radar can develop contacts and analyze their movements with plenty of time to submerge before they can possibly detect you. If you wait until they've passed overhead and are far enough away not to detect you, about five minutes after you submerge, you can just pop right back up to the surface without even checking. Why would that work? Your radar has enough range to detect any plane that could be five miles away when you surface. You already know there are none and are perfectly safe as you have not been submerged long enough to ruin your combat awareness.

Fourth, many battle operations are best conducted on the surface, including deck gun operations, initial nighttime approaches and even torpedo attacks. Being on the surface means your sub is at it most maneuverable and nimble configuration. Often you can shoot torpedoes, turn tail and run away on the surface at 20 knots with no problems at all. If you're underwater and they get on top of you, you are in for a long and dangerous interval of being the hunted, not the hunter.

The submarine is to hunt. Hunting means maximum time on the surface.

U-Boats were the hunted. The Type XXI was designed to operate best in ostrich mode, afraid to poke her head above the surface, which was completely controlled by her enemies. With total domination of air and sea by the Allies, the Germans had no choice but to optimize for the only place they could operate with any safety: underwater. In doing so they surrendered their offensive capabilities, but survival was their goal, not victory. For that the Type XXI was a great design. Well, it might have been a great design because it was never used enough to determine its reliability. It could have been a total dog and they never would have known. My guess is that they would have been sticking their fingers in holes in the dike for the entire first year of operation and only 18 or 24 months into operational use would the Type XXI have begun to show what it was good for.

Superboat it wasn't. It was merely the best thing they could come up with to prolong an inappropriate use of the submarine as a weapon in the Battle of the Atlantic--a battle never winnable by German submarines without control of some ocean surface areas and air superiority in coastal approach zones.

Admiral Daniel Gallery's method of location (snorkels could be located easily by radar), drawing an operational radius and covering that circle until the sub popped up would have worked just as well for a Type XXI as it did for a Type VII. That snorkel would have gone down with a couple of bombs or even a strafing run, reducing the Type XXI to a very limited range. Allied control of sea and air was the end of submarine operations no matter what.

Interestingly, after the war, US Boats were fitted with Guppy I conversions with underwater optimized hull modifications. They achieved higher underwater speeds than the Type XXI with no alterations to batteries or electric motors. Later modifications to Guppy II with higher battery capacity and even more streamlining outperformed the Type XXI in all aspects. These were still trivially modified fleet boats, showing that the fleet boat operated they way it did by carefully chosen design, not because the US Navy was behind the Germans in submarine design capability.

[Bilge_Rat]

RR did an excellent summary.

Clay Blair who was a submariner in WW2 and personally visited a type XXI described its issues in his books on the U-Boat war. I dont remember the whole list, but basically the problem was the fact that the design could not be fully realized with 1945 technology. For example, it may have had a high submerged speed, but the batteries could only maintain that for a short time. The noise from the snorkel drowned out the hydrophones and the vibration made it impossible to use the scope at speeds over 2-3 knots. The ones that were built had been crudely put together and it was doubtful they could dive very deep.

However, the XXI design was copied and formed the basis of most of the Soviet post war diesel sub fleet, notably the Whiskey class:

[Platapus]

http://www.subsim.com/radioroom/show...ight=blair+xxi

Read post #6 for a discussion on the evaluation of the XXI sub.

It "could" have been the best submarine, but one has to evaluate it the way it was constructed and designed. It had potential, but had some serious shortcomings that may have been able to be corrected in the Type XXIb if the Germans had time to get a second modification out.

[Rockin Robbins]

How long did it take for the US fleet boat to become a great submarine? They had the luxury of developing in peacetime and still had lots of fatal errors to overcome. During the war they continually whittled down the conning towers as they realized it was more important not to be seen than it was to see better. Those subs were not designed on a piece of paper but by fatal mistake after fatal mistake changing the original design.

Why would the Type XXI be any different? If it had been fully operational in early 1944 it still would have not been productive by the end of the war. What you don't know WILL hurt you. Somehow we've deified the thing and it was just a collection of future scrap metal like every other machine.

There was a Type XXI which became operational in the West German navy and I'd be interested in the history of that boat to see what they did to make it work. I'll bet it was a lot!