Milchkühe, why so small?

[Jimbuna]

I think it hard for such a huge cumbersome target to remain undetected for long, especially after the Atlantic air gap had been 'bridged'.

[Subnuts]

Originally Posted by ikalugin

Typhoon had both the proper shape hull and a nuclear power plant. For a forties sub you are looking into some serious issues with electric motors even if someone does get a smart idea to make the sub look like a torpedo and introduces shnorkel early.

According to Norman Friedman's US Submarines Through 1945, in 1920 the Department of Construction & Repair designed a series of massive cruiser-type submarines displacing over 8,500 tons. The biggest was 625 feet long, displaced 20,000 tons, was powered by steam turbines, had four boiler rooms, and had six-inch armor over the conning tower, 12" gun turrets, and sides. There would have been five pressure hulls, three in the top of the hull, and two on the bottom.

Ridiculously big submarines were on the drawing board back then, but I imagine it would take 15 minutes to dive a boat that size, and a single 500-pound bomb would probably render it unable to dive.