The claim that an all-submarine German fleet in the 1930s would automatically have won the Atlantic war overlooks the predictability of a single threat. The scenario assumes mass production of Type VII boats, with Type XXI excluded as an option for that period. It would let Britain concentrate construction, crewing, and convoy defence on anti-submarine warfare. The treaty exemption described here covered vessels below 2,000 tons, not designed to exceed 20 knots or carry torpedoes, creating room for sloops and Flower-class corvettes. Such escorts were easier to build and crew than submarines. A submarine normally had to approach the convoy, giving its defenders a positional advantage, although escorts could still fail and submarines could penetrate the screen.
Chapter · 32:24-34:20
Why an all-submarine fleet is a one-dimensional threat
A German fleet built entirely around Type VII submarines would have announced one threat model and allowed Britain to concentrate construction, crewing, and convoy organization on anti-submarine warfare.