Why battleship money could not instantly become U-boats

What if Germany had built about 150 U-boats instead of Bismarck and Tirpitz?

Germany would need enough submarine-building facilities and infrastructure, while Britain could respond to the visible change by building more sloops.

The proposal replaces Bismarck and Tirpitz with about 150 U-boats. A direct conversion of battleship tonnage into that number of submarines is questioned. Germany also needed enough shipyard facilities and supporting infrastructure to construct them. Its limited maritime industrial capacity constrained both capital-ship and submarine building. A visible expansion of the U-boat force would also give Britain warning, and greater British emphasis on building sloops is suggested as the likely response.