Countering the U-boat threat

Q-ships

Introduced in 1915

Merchant ships secretly armed with guns

Sunk roughly 10 U-boats and damaged another 60

Lost relevance with intro of convoys

Convoys

Introduced by Maclay in May 1917

Roughly 20 merchant ships escorted together by 6-8 destroyers

Started in NA but quickly extended to North Sea

27 lost out of roughly 9k, compared to 356 when sailing independently

Depth charges

Underwater explosives

Intro in 1916

Destroyed 16-37 U-boats but mostly used to confirm kills

Improved with the intro of depth charge thrower in 1917

SONAR

Invented by Paul Langevin in 1915

First form was the hydrophone which used the sound of engines and propellers to locate - extensively used from 1917

1918 intro of ASDIC which sent out sound waves to locate

Mines

Biggest killer of U-boats - 48 confirmed

Created belts denying access to certain areas e.g. 70k being laid by US in the North Sea in May 1918, and English Channel

Combined with boom nets to protect harbours and block ships

Aircraft

From Jan 1918 60% of shipping losses were within 10m of the shore

Over 100 airships used to follow convoys, foricng the U-boats to dive

Seaplanes e.g. Catalina used to hunt U-boats