Submarines are framed as strategic insurance: boats spread across an ocean route can make passage dangerous without controlling the sea. Interwar submarines were especially useful for defensive sea denial, although the Battle of the Atlantic made their offensive role more familiar. British confidence in ASDIC rested partly on exercises with bounded areas and obvious targets, unlike dispersed convoy operations in the open ocean. Aircraft and other detection assets made surface travel increasingly hazardous for submarines, but did not solve the escort problem. The gap between a promising detection technology and realistic peacetime testing is the main point.
Chapter · 0:52-2:45
Submarines as sea-denial insurance
The opening frames interwar submarines as defensive sea-denial assets and questions whether controlled ASDIC exercises proved enough for open-ocean convoy warfare.