Could Germany have built a large battle fleet and more than a thousand U-boats, and why did Britain not answer the submarine buildup with masses of escorts before the war?
Short answerNot without first expanding shipbuilding capacity, and Britain had to prepare simultaneously for different threats from Germany, Italy, and Japan.
NotesThe Battle of the Atlantic appears here as a procurement problem rather than a simple hindsight exercise. German yards could not produce a large balanced battle fleet and a thousand submarines without first expanding the industrial capacity that historically allowed U-boat output to grow. British planners had to prepare for different combinations of threats from Germany, Italy, and Japan rather than optimize the fleet for a single German commerce war. The unexpected fall of France and occupation of Norway then gave German naval forces access and opportunities that prewar Royal Navy planning had not considered likely.