Which single Allied submarine type would be most useful if both Germany and Japan had to adopt it?
Short answerThe Gato class, because its range and size can cover both German and especially Japanese operating requirements.
NotesA common design has to cover both German and Japanese missions, including long Pacific patrols. The U class is too small and short-ranged for many of those tasks. The T class is attractive, but its endurance and cruiser-submarine characteristics are judged insufficient for the whole requirement. Gato is therefore the principal choice. A second suggestion introduces large Dutch submarines, and the O 21 class is identified as another good option after a brief discussion of K XIV-class boats.