HMS Periwinkle illustrates that a useful ocean escort did not need to approach the treaty's 2,000-ton ceiling. The Flower-class corvette displaced roughly 925 long tons yet proved valuable in the Battle of the Atlantic before larger frigates became available. Its essential package was a seaworthy hull, ASDIC, depth charges, and guns against aircraft, torpedo boats, and surfaced submarines. Ahead-throwing anti-submarine mortars and later homing torpedoes would improve the attack, but depth charges and ASDIC were already sufficient to justify building the ships. Because one escort might maintain sonar contact while another made the depth-charge run, success depended on having enough hulls rather than one exceptionally powerful ship.
Chapter · 33:17-35:00
ASW needs hulls for contact and attack
Flower-class scale was adequate for Atlantic escort work, but effective ASDIC tactics often required one ship to hold contact while another attacked.