Allied navies divided scarce destroyers across the U-boat war

The submarine threat grew faster than the Allies could supply destroyers and specialized sub-chasers to every theater. American destroyers assumed a large share of anti-submarine work around Ireland, while Japanese forces supported the campaign in the Mediterranean. That division allowed the Royal Navy to concentrate more destroyers on east-coast convoys, barrage duties, and continued support of the Grand Fleet. Early listening equipment existed, but effective ASDIC had not yet transformed the hunt, so coverage still depended heavily on scarce hulls and crews. Allied contributions therefore affected naval operations far beyond the waters each navy patrolled.