Operation Catapult. Admiralty gives Vice Admiral Somerville explicit instructions to secure the transfer, surrender, or destruction of the French warships at Mers-el-Kébir, Algeria, with no concessions given to the French - they either accept the British terms or face destruction. Somerville’s Force H consists of battleships HMS Valiant & HMS Resolution, battlecruiser HMS Hood, aircraft carrier HMS Ark Royal, cruisers HMS Arethusa & HMS Enterprise and 11 destroyers.
U-99 is again subjected to friendly fire. Leaving Wilhelmshaven, she is attacked by a German aircraft with 3 bombs. U-99 crash-dives and collides with the sea floor, causing minor damage.
U-boats sink 3 ships Southwest of Ireland. U-51 sinks Royal Navy decoy ship (SSV) HMS Edgehill (with concealed armament of nine 4in guns, four torpedo tubes and a buoyant cargo to help keep her afloat if hit). Due to Edgehill’s buoyancy, it takes three torpedoes to sink her. http://www.uboat.net/allies/merchants/ships/394.html
U-47 torpedoes British SS Empire Toucan which breaks in two (3 killed). 31 crew are rescued and landed at Plymouth by destroyer HMS Hurricane which scuttles the floating aft section. http://www.uboat.net/allies/merchants/ships/393.html
U-26 sinks Greek steamer Frangoula B. Goulandris (6 lives lost, 32 survivors). http://www.uboat.net/allies/merchants/ships/395.html
Italian submarine Rubino is sunk by Short Sunderland flying boats of RAF 201 Group in the Ionian Sea between Italy and Greece. RAF flying boats pick up some survivors. Off Tobruk, Italian submarine Sirena is damaged by Short Sunderlands of RAF 230 Squadron. West of Crete, Italian submarines Uebi Scebeli and Salpa are damaged by British destroyers HMS Dainty, Ilex, Defender & Voyager. Uebi Scebeli sinks slowly and the crew is rescued by HMS Dainty.