Italian submarine Bagnolini sinks British cruiser Calypso south of Crete.
The British submarine Odin is sunk by the Italian destroyer Strale in Gulf of Taranto.
The British submarine Grampus is sunk by four Italian torpedo boats off Syracuse, Sicily.
Heavy units of the British Navy, code named Force H (Somerville), launch an attack (Operation Catapult) on the French fleet stationed at Mers-el-Kebir near Oran in Algeria, sinking the battleship Bretagne and heavily damaging the battleship Provence and the battlecruiser Dunkerque. 1,300 French sailors are killed and hundreds wounded.
In retaliation for the British action at Mers-el-Kebir, Vichy French warships based at Dakar capture 3 British merchant ships, while French aircraft stationed in Morocco attack British shipping off Gibraltar.
A French naval squadron that has sought refuge at Alexandria is disarmed and interned by the British Navy.
Swordfish aircraft damage the French battleship Richelieu at Dakar after the French reject demilitarisation proposals.
The British and Italian fleets make contact at Battle of Cape Spartivento. The British force includes 1 Aircraft Carrier and 3 Battleships, while the Italian squadron under Admiral Campioni consists of 2 Battleships, 6 heavy and 12 light cruisers. The Italians brake off contact after their flag ship Giulio Cesare is hit and damaged, although they still claim a naval victory.
The Italian Cruiser, Bartolomeo Colleoni is sunk off Cape Spada, near Crete by HMAS Sydney.
The British Battleship Valiant, the Aircraft Carrier Illustrious and two Cruisers leave Gibraltar bound for Alexandria to reinforce Admiral Cunningham's Mediterranean fleet.
A British convoy, under heavy escort, sets sail for Malta from Alexandria. Admiral Cunningham hopes to provoke the Italians into a fleet action. The Italian fleet puts out to sea, only to return to port at Taranto prematurely without seeing action.
The Admiralty announces the recent sinking of two Italian submarines.
Another heavily escorted supply convoy sets sail for Malta from Alexandria. However, bad weather stops the Italian fleet from putting to sea and the convoy arrives safely. Only the escorts return trip to Alexandria, they are attacked by a force of Italian Destroyers and Torpedo boats. No casualties are suffered by the Royal Navy, but the Italians lose 2 destroyers and 2 Torpedo boats sunk and 1 Destroyer damaged.
Italian submarine Toti sinks British submarine Rainbow.
The British Fleet launches an air attack against the Italian fleet at Taranto. Swordfish aircraft from the Aircraft Carrier HMS Illustrious damage three battleships, two cruisers, two destroyers and two auxiliaries craft. This British victory, forces the Italians to temporary withdraw their big surface units to the safer ports on the west coast of Italy.
The British Admiralty decides to send the Battleship Ramillies and 2 Cruisers from the Mediterranean fleet to reinforce the Atlantic fleet. They are to sail to Malta with a supply convoy, link up with Force H and then sail onto Gibraltar. Just as the reach the rendezvous point, Ramillies, the 2 Cruisers, the Aircraft Carrier Ark Royal and 10 Destroyers are intercepted by Admiral Campioni's squadron of 2 Battleships, 7 Cruisers and 16 Destroyers. However, as soon as the Battleship Renown from Force H joined in, the Italians withdrew with 1 Cruiser and 2 Destroyers damaged, while the British suffered damage to the heavy cruiser HMS Berwick.
Italian Naval Chief resigns, to be replaced by Admiral Campioni.
The Admiralty decides to transfer another Battleship, HMS Malaya to Force H from the Mediterranean fleet. Again this was to be accomplished by escorting a convoy to Malta and linking up with units of Force H for the journey to Gibraltar. No losses were suffered to enemy action although a Destroyer was sunk when it hit a mine.