The potential of the new Typ XXI Uboot

The Typ XXI Uboot, in the perceptions of the Nazi-German leadership - Hitler and Dönitz - held the potential for reversing Germany's fortunes big time. Tremendous effort in men and materials went into getting the boats 'front ready' ASAP. There is good bit of information on these submarines in print now, and I'm interested in hearing others' evaluation of their potential for reversing the course of the war. Here are a couple of major factors: [1] operating range and endurance at sea, torpedo load... very great, but limited. [2] ability to operate silently and undetected by allied ASW vessels and aircraft in an open ocean environment appeared to offer great promise, and allied response would take time. [3] any other possible allied countermeasures. [4] were the allies in mid 1945 still so vulnerable at sea that a slaughter of merchant shipping would have reversed the course of the war?

Was meint ihr denn? Lou

 

A few further questions:

I know they were very quiet and quite fast, but they were still built of ferrous metal. Would they not still have been vulnerable to detection both by MAD gear (Magnetic Anomaly Detectors) and active sonar pinging? (I suppose if they'd been coated in an acoustically absorbent material, but I've never heard that they were.)

My initial guess is that the Germans were barking up the wrong tree. Allied anti-submarine warfare capabilities had advanced to the point by 1945 that it would have been very difficult for the Germans to make enough of a dent in allied shipping to justify the no doubt enormous cost of the boats and crews. The U.S. was regularly using ASW blimps and long range aircraft equipped with MAD gear. There were enough CVEs available to escort an enormous number of convoys with great strength of aircraft. We were awash in destroyers, corvettes, and other ASW capable escorts.

I just don't see math in building the subs. They still have to run shallow for their attack, as we'd figured out how to decoy the acoustic torpedoes. They still have to snorkel and run the diesels to recharge the batteries, no matter how many of them they have. (Diesels which will be audible to anything and everything nearby.) I'd guess they're still going to reflect a ping. And with that many ears on that much sonar gear, somebody's going to notice the echo eventually.

Anyway, I look forward to hearing more. I'll have to dig around a bit myself, but you raise some interesting questions.

 

Good thinking. Yes, noisy diesels, good ping and MAD targets they would remain. However, higher capacity and larger storage batteries meant both higher underwater speeds and greater endurance on their much more silent electric motors. The ASW battle would for a time swing in their favor.

Apart from these technical improvement in the submarine itself, which is one aspect of the topic and worth a great deal of discussion, there is the wider picture of the conduct of the war and whether even a major offensive of super-Uboats could cause the Allied nations to give in. I think that after a certain point, say 1 November 1944, such a reversal could no longer be achieved by the Germans.

Pick a date... let's say 1 March 1945. In the first 10 days of March the sinkings by the new Uboats at large in the Atlantic soars to twice that of March 1943. What are the Allies' options? One, I think, is to simply cut off the supply of targets. No more sailing, singly or in convoy, eastbound or west. None, zero. It will be three weeks before the all existing ships at sea reach port, but then the campaign is over. No targets.

Yes, the land and air offensive on the Continent is almost immediately short of fuel and essentials. SHAPE says simply to his generals to curtail all operations not directly aimed at crushing the German political machine in Berlin. Set all else aside on all fronts. Crush Berlin and the NS headquarters and leadership and the war is over in Europe and the Uboats worthless. How long could Hitler and his pals continue on?

Perhaps to the second week in May is my guess, if that long.

Remember, the Russians were across the Oder already, and the Western Allies deep into Germany. The terribly weakened Germany Army would have fought well, but could not have resisted a focused thought from both East and West.

There were other options as well.

Flags

 

By 1945 the Allies had just entering production weapons and sensors that would have made the Type XXI marginally more effective than previous German boats. These included:

Scanning sonar. Almost all WW 2 sonar had a 9 to 11 degree cone-like sound projection and return. They worked much like a searchlight might. The operator had to scan a particular arc segiment then move the ocillator and scan the next segiment. This was slow and tedious work. The chances of missing a target were fairly high.
By 1945 the Allies had just entering production sonars that could perform either a rapid scan of each arc segiment or ones that projected an "omni-directional" signal and could process the return signatures. They also had "nodding" sonars that allowed for some degree of accuracy in depth estimation.

New ahead throwing weapons were also about to enter service. The British had Squid / Limbo just coming on line. These three tube mortars could fire an 11" depth charge ahead of a ship and used in pairs put down a fairly nasty pattern that would be difficult to evade even by a Type XXI.
The US had Weapon Alpha in development. It rapid fired a round similar to a Squid / Limbo and could also lay down a pattern over most of the forward 180 degree arc of a ship carrying it.
Trainable Hedgehog was also coming on line. Like Weapon Alpha it was no longer confined to just ahead fire. Thus, a ship using it could fire a pattern over most of the forward arc of the ship.

Allied aircraft were already carrying passive sonobouys and an active one was about to come into service. Using the Judy technique (dropping an explosive charge for echo ranging) the passive buoys could be used to detect a quiet boat.

The Allies also had ASW homing torpedoes just coming into service as well. These too would have made any advantage a Type XXI had in speed marginal. At this point the Germans (and everybody else) hadn't paid much attention to quieting submarines. So, the Type XXI was fairly noisy. Another failing of it was poor workmanship. These boats were fabricated in subassemblies and then put togeather on a slip. Unfortunately, the tolerances were often sloppy and the parts didn't fit well. This and the assembly methods left alot of weak points in the boats.

The biggest problem the Allies face is that many of their escorts, particularly the British ones, are too slow to effectively combat a Type XXI. The US isn't using that many frigates and corvettes but the British are. The Flower class would have become largely worthless as they could no longer run down a Type XXI submarine. US destroyer escorts (the prefered type for the USN) could still manage with their speed of 28 knots.

 

Well put, even with the "streamlined" assembly line methods, Speer only managed to get about 120 of this type launched didnt' he? And if they failed or had badly fitting parts, they could fail at depth where the older "hand-made" boats could exceed their estimated "crush depth".

The advantage in this type would have to come much earlier in the contest at sea to have made any difference. And since the "need" for the type wasn't seen until it was too late, they couldn't/wouldn't be developed any sooner than they were.

I seem to recall that it still took something like two years to go from design to first launch didn't it? If they started in 1942 for a 1944 delivery, to advance it would mean the Kreigsmarine wouldn't have the experience to draw upon which made the XXI appear.

Development cannot go from "learning" to "fruition" without the intervening learning process. It just doesn't work like that, the Thresher is a good example.

 

These are all good points, but as Clay Blair points out in the second volume of his study of the Battle of the Atlantic ("Hitler's U-Boat War"), the potential combat value of the Type XXI U-boat was virtually nil when it first appeared in combat.

This was because the Allies had finally managed to employ enough long range patrol aircraft to adequately cover all of the Atlantic convoy routes, as well as the areas the U-boats would have to transit on their way to and from the combat zones. This, coupled with surface hunter-killer groups, forced the U-boats to make the entire voyage submerged at minimal speeds. Transit times for the U-boats were measured in weeks, leaving just a matter of a few days for patrolling against the convoys. Furthermore, contrary to claims of the "what-if" boys, the Type XXI was NOT a "true submersible"; it required the use of diesels (combined with snorkeling) which left the Type XXI vulnerable to normal ASW tactics and weapons much of the time. Blair, himself a WW II submariner who inspected one of the captured Type XXI's at the end of the war, is dismissive of the "advanced" German sub technology, if the last chapter of the second volume of his book is any guide.

It was true that the extra battery capacity gave the Type XXI a limited period of high underwater speed, but this was not sufficient to overcome the Allied ASW proficiency which prevailed after 1943. Moreover, the Type XXI boats suffered from poor design, shoddy construction, and batteries which had a short life due to the demands of high underwater performance.

 

It should also be pointed out that as the US found out post war these batteries were prone to catastrophic failure. Pushing them with extended high speeds while under battery power could tend to increase the likely hood of such catastrophic failure. I believe the failure mode was hydrogen production and subsequent ignition. Not good in most cricumstances but really bat in a confined vessel under water especiallly attempting to remain undetected.

 

A few other post war findings on the Type XXI:

The AA armament installed on the sail in two small turrets (one at each end) were death traps for the crew if the boat had to emergancy submerge. They could never get out in time to survive.

The surfaced bouyancy and submerge rate were such that the sub was really dangerous if it were to suffer flooding unexpectedly. The high sink rate made for a quick diving time but it also meant the boat would sink like a stone if flooding occured. In fact, I think the Bundeswher had one in the 50's that did just that during a training exercise if I recall correctly.

One of the better points on the Type XXI was the sonar. The Gruppenhochgerat was a major improvement in sonar using a 24 head array that could make detections at longer range and give sufficently accurate firing data to allow a fully submerged attack on a surface ship.

 

It wouldn't have mattered one bloody bit how many Type XXI's the Germans had in March of 1945. Say they had 100? So what?

The Russian were knocking in the door to Berlin by then.

 

That's correct, and US naval officers who examined captured German U-boats (and not just Type XXI's) postwar were astonished at the fragility of German U-boat batteries. It is theorized that many German U-boats were destroyed when their batteries were shattered by Allied depth charging, bombing, and "hedge-hog" attack, and this would also have applied to Type XXI's had they managed to get into combat.

The Type XXI was poorly designed, especially the hydraulic systems such as steering and the snorkel-raising gear. Some of the hydraulic lines actually were outside the pressure hull which led to excessive corrosion, leaks, and, of course, meant that the systems could not be repaired by the crew. The Type XXI were powered by a new diesel engine which was super-charged to produce the required horsepower, but the supercharger was so poorly designed and built, and ran so hot that it had to be disconnected in the interest of safety. This left the Type XXI badly underpowered.