The 1939 war-emergency orders appear to have drawn on standing plans prepared for different warning periods. Research and design work were also converging on a major submarine order around 1940. A proven boat that could enter service near the expected danger window offered rapid mobilization without waiting for an entirely new type. Delivering it close to the anticipated 1942 risk period also reduced the time available for an opponent to study the design and prepare counters.
Notable Point · 19:48-22:24
War-emergency orders and Britain's 1942 risk planning
The return to S-class construction is tied to standing mobilization plans and a Royal Navy expectation that the critical war-risk period would begin around 1942.