The number of U-boats built is not the same as the number available on patrol. Training, transit, repair, and especially combat losses reduce the operational force, and German attrition eventually exceeded sustainable replacement. British mobilization also differed sharply between the two world wars. During the First World War, the crash escort program began only in 1916 and convoy implementation came late enough to create a severe crisis in 1917. Before the Second World War, escort programs were already beginning in 1938-39, giving the convoy system a much stronger starting position. Advance procurement and operational availability matter more than headline production totals.
Notable Point · 2:25:21-2:27:48
U-boat force generation and the timing of escort mobilization
A force-generation discussion separates submarines built from boats on patrol and compares the late First World War convoy response with prewar Second World War escort construction.