In late March 1941, as British ships of the Mediterranean Fleet covered troop movements to Greece, Mavis Batey, a cryptanalyst at Bletchley Park, made a breakthrough, reading the Italian naval Enigma for the first time.

[3] As always with Enigma, the intelligence breakthrough was concealed from the Italians by ensuring there was a plausible, visible reason for the Allies to have detected and intercepted their fleet.

[4] As a further deception, Admiral Cunningham made a surreptitious exit after dark from a golf club in Alexandria to avoid being seen boarding his flagship, the battleship HMS Warspite.

He had made a point of arriving at the club the same afternoon with his suitcase as if for an overnight stay, and spent some time on the golf course within sight of the Japanese consul.

[5] The Allied force was the British Mediterranean fleet, consisting of the aircraft carrier HMS Formidable and three Queen Elizabeth-class battleships, Barham, Valiant, and Warspite.

The Italian fleet was led by Admiral Iachino's flagship, the modern battleship Vittorio Veneto, screened by destroyers Alpino, Bersagliere, Fuciliere, and Granatiere of the 13th Flotilla.

The fleet also included most of the Italian heavy cruiser force: Zara, Fiume, and Pola, accompanied by four destroyers (Alfredo Oriani, Giosuè Carducci, Vincenzo Gioberti, and Vittorio Alfieri) of the 9th Flotilla; and the heavy cruisers Trieste, Trento, and Bolzano, accompanied by three destroyers (Ascari, Corazziere, and Carabiniere) of the 12th Flotilla.

Joining them were the light cruisers Luigi di Savoia Duca degli Abruzzi and Giuseppe Garibaldi (8th division) and two destroyers of the 16th Flotilla (Emanuele Pessagno and Nicoloso da Recco) from Brindisi.

[9][10] As they had not reduced the distance significantly after an hour of pursuit, the Italian cruisers broke off the chase, turning to the north-west on a course to rejoin Vittorio Veneto.

[9][13][14][15] A series of photographs taken from HMS Gloucester showing Italian salvos falling amongst Allied warships was published by Life magazine on 16 June 1941.

[16] A second aerial attack at 15:09 surprised the Italians; Lieutenant-Commander John Dalyell-Stead (DSO) was able to fly his Albacore to within 1,000m of Vittorio Veneto before releasing a torpedo which hit her outer port propeller and caused 4,000 long tons (4,100 t) of flooding.

[19] Williams was subsequently awarded the Distinguished Service Cross, primarily for the part he played in bringing about the ensuing naval engagement.

The squadron did not start to return towards Pola until about an hour after the order had been given by Iachino, officially due to communication problems, while Vittorio Veneto and the other ships continued to Taranto.

[22] Two Italian destroyers, Vittorio Alfieri (flagship of the flotilla commander, Captain Salvatore Toscano) and Giosuè Carducci, were sunk in the first five minutes.

The other two, Gioberti and Oriani, managed to escape in a smoke screen, the former with heavy damage, after being chased and fired at by the British destroyers Griffin and Greyhound.

The only known Italian reaction after the shocking surprise was a fruitless torpedo charge by Oriani and Gioberti and the aimless fire of one of Zara's 40 mm guns in the direction of the British warships.

[7] Allied casualties during the battle were a single torpedo bomber shot down by Vittorio Veneto's 90 mm (3.5-inch) anti-aircraft batteries, with the loss of the three-man crew.

[28] For reasons of secrecy, code breakers at the GC&CS were very rarely informed of the operational effects of their work, but their impact on the Battle of Cape Matapan was an exception.

[1] Admiral John Godfrey, the Director of Naval Intelligence, stated: "Tell Dilly that we have won a great victory in the Mediterranean and it is entirely due to his girls".

[1] There is still controversy in Italy regarding the orders given by the Italian Admiral Angelo Iachino to the Zara division to recover the Pola, when it was clear that an enemy battleship force was approaching rapidly from the opposite direction.

Only later, after Dilly's rodding method was demonstrated by Mavis Batey to the Admiral in charge of naval history, were Italian official records corrected.