The German Navy promised that unrestricted submarine warfare could destroy 600,000 tons of merchant shipping each month. It met or exceeded that figure only from March through June 1917. Convoys, escorts, radio-informed routing, and air patrols then deprived U-boats of the exposed targets needed to sustain the campaign. ASW success could therefore come from denying opportunities: aircraft did not need to sink every submarine if their presence kept boats submerged or away from shipping.
Notable Point · 25:30-26:51
Why German U-boat tonnage promises collapsed after mid-1917
Germany reached its promised 600,000-ton monthly sinking rate only briefly before convoying and air patrols reduced U-boat opportunities.