1. Just one thing to note. There was no room in the Type VII for more battery cells. In the Type IX, the Germans would have to sacrifice an engine. Since German tactics dictated surface torpedo boat like attack in a swarm or a pack and then dive to escape, that would not exactly be "smart" to rob an U-boat of its surface tactical speed. There is something called aggregate tactical speed of U-boat, torpedo and target. As an average in the battle of the Atlantic, this was about 5-6 m/s or 10-12 knots. Angle solutions for the typical German torpedo yielded aspect differences of no more than 140 degrees and run times of no more than 200 seconds off set run time on a rather average family of weapons rated at no more than 15-20 m/s (30-40 knots) and with run times at 800 seconds at 15 m/s or 400 seconds at 20 m/s. Note that the slow setting was for aggregate merchant vessel/U-boat tactical speed at (6 m/s) 12 knots, and the expected aggregate escort/U-boat tactical speed at about 6-7 m/s (16-18 knots).
2. There is a flaw in the thinking that suggests one needs a faster U-boat with a snort. The snort is useful as a battery recharge feature in an LRMP dense environment, One might like a quiet muffled and rafted Stirling cycle engine as the recharge engine though instead of a diesel: that is
a quieter U-boat. In addition one might like to have a torpedo with a seeker in it that uses target noise or wake to home in on aforesaid target. The Germans develop pattern runners and they (1933 onward) try to develop an acoustic [self guided weapon] torpedo (one of the reasons for the G7e), but...
3. They are not very successful because they scatter their efforts, and do not understand what they try to accomplish. They are not very good systems analysis engineers. As has been known since the first WW I about guided weapons. (UK and France op-research in the 1920s.) If you want to improve chances in PH (hit) or PK (kill) and do that function most economically, then the solution is not the launcher, it is the projectile or missile. This is kind of obvious. No-one, except the Germans, despite knowing the solution, even tries for an acoustic or wake homing torpedo. The reasoning was simple at the time. The torpedoes possible (or so it was thought) were too noisy to make hydrophones work and with the vacuum tube technology available, it was not likely to work as the electronics would fail.
4. The Germans, British and Americans did get excited about maybe using magnetic influence to set off torpedoes. Mining effect. Close enough is good enough. Break keels, yoah! This was based off WW I German magnetic influence mines. Should have worked, but the short version is that Earth is a lumpy irregular magnet, and all three navies leaped to the wrong solution about how to use that magnet to set off their fusing mechanisms. Later in 1945, too late to do any of them any good, they all figure out self generated magnetic influence features and a rheostat is the way to make a magnetic influence feature work, but if you want to read about it in detail, (
...Those Marvelous Tin Fish: The Great Torpedo Scandal Avoided)…
5. Meanwhile, there is the acoustic torpedo and the wake homer. The Germans have been working on the acoustic torpedo for quite a while. They finally get it to work around 1944-45 and start turning British escorts into "banana boats" with T-4 G7es that prang British escorts in the props and artificially hog the British ships by raising sterns. There is some question whether these are contact fuse hits or if the German magnetic influence feature sets off the fish early and the bubble lifts the frigate's stern. My guess is that the influence feature is at work because a lot of these banana boats survive. Not too smart. Wake homer (active sonar pings off the bubbles formed in a ship's wake flow and the fish follows the echoes) is a bust for the Germans. Note that all the fancy wonder weapon torpedoes are finicky, the electronics involved is fragile and the weapons are expensive? The seeking guided torpedoes are "rare" with a MFR of about 50% for the Germans.
6. Enter the United States. Worst torpedoes in the world. Circle back on you, run wild nose wander right, run deep, impact hammer fuses do not work, magnetic influence circuits go off early. Lots of clangers, target run unders or miss rights and prematures. Wrong tactics too, but the point is that the torpedoes MISS even when angle solutions and depths are correct. Enter HUSL. (I love puns.) Harvard Underwater Sound Laboratory. They are the sound version of the MIT Rad Lab. These guys include systems analysts. Despite US Navy and Congressional politics which impede solutions on the current weapons in use,
these boys and girls figure out how to make an acoustic torpedo work in mere months. Thanks to the BRITISH who capturfed it and the Germans who supplied the weapon by accident, a complete U-boat with working electric torpedoes is also provided. OOPS. The Mark XVIII copied from the G7e is cheap and plentiful, and with a working warhead and able to gyro steer into a ship is good enough to kill freighters. The CUTIE, the submarine version of FIDO, (1944) starts killing Japanese escorts (as in SINKING them) about the same time the Germans turn British frigates into banana boats. 24 months for that one. CUTIE is not plentiful, but it is not all that rare either. The Mark XVIII with an acoustic seeker a true heavyweight guided weapon is 1945.
7. The upshot, primarily, is that the Americans develop FIDO (independent of German or British influence) in about 12 months, and the Allies start to kill U-boats with it around 18 August 1943 or 6 months later.
It would not have mattered if the Type XXI had come into service. As I noted earlier, the Germans screwed up the Type XXI's screws. The FIDO is still just fast enough to catch it on battery in a hammer and anvil attack profile. And its faster cousin, the Mark 32, (postwar deployed) is on its way (1946?).
The Type XXI without an abundant source of guided weapons and still stuck with wrong tactics is not going to be the convoy killer the Germans hope it is. That is the whole point. The Americans were confronted with the same exact problems the Germans had. The Japanese merchant fleet had to be killed and the American subs were not getting it done. Design a new kind of sub as the Japanese ASW improved? (Oh yes; it improved.). No. The Americans had 20 different torpedo programs going. Not submarines...
torpedoes.
Post-war these were rationalized down to fewer different types, including the finally debugged Mark XIV (freighter killer with a now working magnetic fuse), FIDO (sub-killer), the Mark XVIII and her anti-ship cousin the Mark 26 (CUTIE), and the Mark 28. But the US still worked on that wake homer, and more cousins to FIDO.
When the US did make her radical break with submarine design, (rather sedately in 1955) it was to obtain an atomic powered submarine for
tactical offensive speed and true submerged operations. GUPPY and the Tenches were just stopgaps and were always so seen.
The urgent effort was still in the torpedoes.
The Germans just never saw it. Maybe it was because their torpedoes were just good enough at the start that they did not see the urgent need in the right place?
seems like there would have been enough reason to revamp their near constant messaging by then?
@McPherson suggested messaging buoys (IIRC, cannot find exact post
It is in the that storyline I manage, where I sank the USS Mudskipper after she kills Shokaku (#701?). In the mid 1930s, the USN developed an automated weather buoy which was dumped over the side of a destroyer or cruiser to radio back to a shore station or a weather ship, local sea conditions. From this contraption, complete with something called a wire loop repeater/recorder, they developed it into a sonobuoy that could be air dropped from a Sunderland or a Liberator and which could radio its findings to a destroyer or an airplane. That was about 1944 in OTL. The same technology was designed into a float line buoy that could mark the position of a downed submarine (SQUALUS disaster 1935.). The free float messenger buoy is just an extension of the available technology. Nothing fancy. The Germans or the British could have done the same. Why they did not (or why the US OTL did not) is curious. I suspect it is because they would have to give up a torpedo space in the racks to stow one and use it. I ITTL did it because it seems kind of necessary to mark the passing of a submarine. The
ARA San Juan could have used one.