... with the early Cold War rapidly getting hot, the American Navy perceives a growing threat from Soviet subs. In both World Wars the danger from 'undersea-boats' was hugely underestimated. Lesson learned; for WW3 Russia builds a large fleet of diesel powered attack subs to counter NATO's larger surface ship dominance. Counter-measure against counter-measure brings Anti-Submarine Warfare 'ASW' to a fine art.
Where would cold-war movie drama be without the classic scene of the technician-dweeb intently 'staring' into his sonar headphones? Listening for the return echo ....... 'BLIINNGGG!'