An escort closing to drop depth charges risked losing its ASDIC contact at precisely the point where the submarine could evade. The preferred answer was a small group, with one ship maintaining the search while another prosecuted the attack. British officers debated whether two or three escorts were required for this contact-holding and attack cycle. The tactic made escort availability part of sensor performance because a lone ship could not hold contact and attack with equal reliability.
Notable Point · 42:37-43:06
Why one escort could not easily destroy a submarine
By 1939 the Royal Navy expected two or three escorts to be needed: one to keep ASDIC contact and another to make the attack.