Exercise 77 biases the lesson on submarine attack

Exercise 77 assigned thirteen submarines to patrol lanes across the path of a screened fleet on 6 April 1938. Exceptionally clear weather let aircraft see submerged boats and surface ships spot periscopes at distances up to seven miles. Twelve submarines fired twelve practice and thirty-six simulated torpedoes; six practice weapons hit, including two that struck ships other than their intended targets. Eight, possibly nine, submarines were detected and ruled destroyed. The submarine commander noted the skippers' limited experience attacking such a large formation, while the fleet commander regarded the event as elementary training that needed repetition. A battleship captain without submarine experience instead emphasized deep attacks using sound equipment alone, which appealed to senior submariners already committed to that approach. The daylight scenario constrained the alternatives and reinforced a doctrine that later hindered American submarines.