ASDIC development began in 1916, and the system entered production in 1922, but it was never regarded as perfect. As an escort closed the target, contact became harder to maintain, so a 1935 exercise paired one ship holding the bearing with another delivering depth charges. The 455-pound charges needed to explode within roughly 15 to 20 feet to have the intended destructive effect. This method required ships that a convoy commander might be unable to spare. Peacetime exercises favored economical destruction of the target. Wartime escort work could justify heavy ammunition expenditure merely to suppress a submarine. Any pursuit had to be balanced against the convoy's primary mission: reaching its destination safely.
Chapter · 6:13-8:22
ASDIC, depth charges, and the convoy mission
Detection and depth-charge attacks posed hard tactical choices because the escort's first duty was moving the convoy safely onward.