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.