Prewar exercises made carrier aircraft appear highly effective at finding submarines because the submarines operated inside restricted areas and followed exercise rules. Those conditions produced false confidence that a submarine could not reach the carrier conducting the hunt. In wartime, ASDIC contact could be lost during the interval before a depth-charge attack, giving a submarine room to evade. The sinking of HMS Courageous exposed both that exercise bias and the poor economy of risking a scarce multi-role fleet carrier on routine anti-submarine patrol.
Notable Point · 40:50-42:19
Courageous and the danger of exercise bias
The loss of HMS Courageous shows how controlled exercises overstated carrier aircraft and ASDIC performance against submarines obeying artificial boundaries.