Early Anti-submarine patrols, Royal Navy, 1939
In the early days of the Second World War, a period sometimes referred to as the “phoney war”, there were significant actions at sea involving the Royal Navy and Germany’s Kriegsmarine. The German U-boats wreaked havoc on the British and French merchant fleets, and the British responded by creating anti-submarine task groups centered around their fleet aircraft carriers, most of which were relatively slow, having been converted from World War One battlecruisers. These carriers were escorted with four or five destroyers or corvettes. The idea was a combined action of carrier aircraft forcing U-boats to submerge, when they would be depth-charged by the destroyers.
On September 17, 1939, with the war but two weeks old, the aircraft carrier HMS Courageous sent two of its escorting destroyers to the assistance of a merchant vessel which reported itself under attack. Unknown to Courageous, it had been stalked for several hours by a submerged U-boat, and when the carrier turned into the wind to launch aircraft it was struck by two torpedoes fired by the German. Courageous sank in minutes, more than 500 of its crew were killed, and the U-boat escaped unscathed. The British Admiralty immediately revised its antisubmarine warfare tactics, withdrawing the fleet carriers from that duty, out of concern for the lethality of the German U-boats.