How helicopters reshape early-war ASW

Regular patrols around Scapa Flow could make Günther Prien's historic penetration against Royal Oak much harder, while Gibraltar patrols threaten submarines entering or leaving the Mediterranean. Clear and shallow Mediterranean waters make visual detection especially dangerous for submarines. If Britain builds several helicopter sloops each year, dozens could be distributed among bases, convoys, and cruiser stations by 1939. A helicopter-equipped cruiser can also scout for submarines and surface raiders without stopping to recover a floatplane, avoiding a vulnerability deeply impressed on the Royal Navy by the loss of Aboukir, Cressy, and Hogue. Rotary-wing aviation consequently becomes a routinely usable fleet tool rather than equipment that captains hesitate to launch.