First off, I want to thank everybody for the healthy response. It beats the usual resounding silence all hollow.
And more training which requires more boats. As it is the Entire U boat arm in 1940 has 54 crews. in 41 250 crews and 350 pa thereafter thats trained so less losses plus survivors.
So if you want 85 boats on station from anywhere that's 255 trained crews re war and if you want them in Type IX thats increasing production from 9 boats to 285.
Not going to happen unless you scrap the entire navy and if you are not building Bismarcks and Graf Spee the brits change their build as well and react differently to events pre war.
I'm not (perforce) saying "Start with 85 on station". (The Pacific Fleet Sub Force certainly didn't start with 65 on station.) I do mean, your average for the duration has to be 85. If you can reduce the transit time, or increase the tonnage/patrol (both possible), that number (obviously) goes down.
It might require scrapping the heavies. It
will change the Allied response; I fully expect it to.
It took 3 years for Germany to achieve the 100 boats 'at sea' that Dönitz had 'wanted' on 8th Aug 42
How much of that was because it looked like the OTL half-measures & diversions to the Med & Norway were working?
One of the biggest reasons for the Uboat's successes was not only large numbers of boats but also the problems the allies had in cracking Enigma for much of 42
I don't buy that, I'm afraid. It wasn't necessary to read U-boat signals to know U-boats were near convoys, & DF would achieve that. (Yes, that change will make it harder for the Germans, not easier...)
the quicker answer that the allies would come to is to throw more aircraft at the problem - something they should have done earlier than they did anyway.
Indeed, & a fairly small number of Stirlings in Newfoundland would have a disproportionate effect--again, not making it easier for the Germans...
Germany in order to win the BotA has to achieve a Uboat build up far far quicker than they did - before the technological, geographical and number advantage of the Allies increasingly enjoy make it impossible (OTL this was probably at some point during 1942 and certainly by May 43)
So I think they have to achieve a crippling loss rate (i.e. mid/late 42/early 43 numbers) and do it by the end of 1941
IMO, the Germans could achieve something close to it later than that. In early '43, the Brits were (AIUI) seriously considering abandoning convoys; better German performance earlier might just lead to it.
Realize that realities of war will change and Britain will inevitably arm merchants and organize convoys. Thus after the initial period deck guns will become useless. However in the early period they can even form the basis of submarine tactics. Thus I’d have a peacetime design focusing on gunnery numbering around 40 subs or so with a wartime design doing away with deck gun completely and focusing on underwater speed.
Prepare for modular design and construction of submarines. Build engines and long build items before the war but without the subs.
Come up with a snorkel sooner if possible. It’s not a revolutionary invention and I’m amazed it too so long for them to adopt it.
Develop a slow, 12-20 kt changeable speed noisemaker torpedo capable of doing zig zag patterns to emulate a mannouvering submarine.
Discover and understand thermal layers and their impact on sonar performance. Train the crews on understanding it and using it to avoid detection or facilitate escape when possible. Understand the underwater performance of submarines and cavitation creation due to X speed at X depth.
Long range Wire guided torpedos allowing the use of periscope and hidrophone to guide a torpedo into target.
Train the crews to perform submerged attacks without use of periscopes. If that is possible design submarines capable of deep strike rather than designs capable of only sub 100ft attacks. Being able to strike from 100 meters underwater would be a great boon.
So much of this demands giant technological leaps, I hardly know where to start.
Deck guns are useful for targets not worth a torpedo, as well as cripples.
Modular design (as others discuss) was a effectively a non-starter.
Wire-guided torpedoes are too sophisticated & expensive, &, for attacking merchantmen, essentially pointless.
Attacks without periscope (by sonar) were USN prewar doctrine. The war proved they don't work: it's impossible to get accurate-enough target bearings. (It requires something akin to
PUFFS.)
A noisemaker torpedo is an absurd waste of resources.
I will say,
schnorchel is a good idea.
Discovering the thermal layers isn't a bad idea, but it presupposes U-boats being under attack by convoy escorts. Most sinkings were unescorted targets.
they should've maintained absolute radio silence, save for emergencies, when transiting to or from patrol areas.
I should have recalled how verbose U-boats &
BdU were...
You're absolutely right. I'd add, "on patrol station".
they still had to attack convoys, at least occasionally
True, but IMO the number of unescorted ships was high enough, it could be a rarity.
Hydrogen peroxide torpedoes combined with reliable contact detonators
Okay, first off, nitpick alert: they're exploders, not detonators.
Why the focus on torpedoes? If they can't hit anything, it doesn't matter how fast they are.
Moreover, if you're firing at a target only doing 10kt, a 50kt torpedo is a waste of effort. So is range of 20mi (or 10), since you can't hit a moving ship at that range anyhow; the fuel is a waste of space. A 25kt torpedo with a range of (say) 8000yd, & a warhead of (say) 2000pd, makes way more sense. (Yes, U-boats won't only be firing at merchants. A handful of fast torpedoes might be needed for opportunity targets, or anti-escort attacks.)
Better, more reliable exploders would be a very good idea--but better firecontrol gear, to achieve more hits (which could, at need, be polished off with guns), IMO is better still. Larger warheads, in connection with better firecontrol, will also produce more sinkings.
Neither requires radical new tech, nor dangerous onboard materials. More to the point, better firecontrol gear can stay secret, so the Brits can't respond prewar--& once war starts, they'll have to realize that's the cause.
How do you achieve it? I'd steal the plans of the TDC, myself. I'd also seriously consider fitting every U-boat with a retractable radar mast & about a 25cm wavelength rangefinding radar. (You have to get that past Dönitz, who seems hostile to new tech...)
Put seaplanes on German U-boats to help find/bomb targets and stop American ariel reconnaissance over the Atlantic.
No, no, no, no no. Seaplanes take too long to erect, are damn near impossible to recover in a sea, are extremely hard to land in a sea, & have to be stowed on deck in a way that makes diving very much slower, not to mention operations more hazardous (if the hangar is punctured, it floods...
)
More milk cows to keep subs out longer.
As noted, time on station isn't actually as beneficial as widely believed.
I watched a Mark Felton Production video on the possibility of v2 rockets being put on subs, allowing the U-boat to target US and British coastal cities.
The gigantic waste of resources the V-2 represents
is another thread.
The use of V-2s against the cities of Britain or the U.S. makes Japan's nuisance shelling of Los Angeles look like a brilliant strategy by comparison.
A dedicated force of long-range maritime support aircraft that will spot and track convoys
That would go a long way, IMO.
Better protection of u-boats while transitting out/into bases, mainly over the Gulf of Biscay. The amount of u-boats lost in the Gulf of Biscay is simply stunning, the Luftwaffe could have done a better job defending them. It will mean however investing heavily on resources.
That's also a really good idea. It reminds me of one of my favorite ideas, intruder attacks on Coastal Command bases. (Impractical? If so, the German air effort might be too high to sustain.)