The Raid on Alexandria (Operazione EA 3) was carried out on 19 December 1941 by Royal Italian Navy (Regia Marina) divers of the Decima Flottiglia MAS (Decima Flottiglia Motoscafi Armati Siluranti), who attacked and severely damaged two Royal Navy battleships at their moorings and damaged an oil tanker and a destroyer in the harbour of Alexandria, Egypt, using Siluro Lenta Corsa, manned torpedoes.

The attacks came at a difficult time for the Mediterranean Fleet, after the loss of the aircraft carrier HMS Ark Royal and the battleship Barham to U-boats, the loss of ships during the Battle of Crete and the sinking of much of Force K on an Italian minefield, the day before the human torpedo attack on Alexandria. Ships also had to be sent to the Eastern Fleet in the Indian Ocean.

The interest of the Regia Marina in small boat warfare lay dormant between 1918 and the diplomatic crisis with Britain over the Second Italo-Ethiopian War 1935–1936. In 1935 and early 1936, Captain Teseo Tesei and Captain Elios Toschi tested a human torpedo in La Spezia on the Tyrrhenian Sea and resumed testing in May. The Ethiopian defeat in 1936 ended the tests but work on assault boats continued. On 28 September 1938, Supermarina ordered the I Flottiglia MAS (1st Torpedo Motorboat Flotilla), based at La Spezia, to establish a research department (the Sezione Armi Speciali (Special Weapons Section) from 1939. The detachment had a few officers at HQ, seven at a confidential base at Bocca di Serchio for human torpedo and frogman training and another six officers to pilot the assault motorboats, of which seven had been built, plus eleven Siluro Lenta Corsa human torpedoes.

On 24 February 1940, the 1st MAS Flotilla and the Special Weapons Section was taken over by Commander Mario Giorgini and in August attempts to use the unconventional weapons began, with little success and the capture of Giorgini in October. On 23 January 1941 Commander Vittorio Moccagatta replaced Giorgini and on 15 March formed the Decima Flottiglia Motoscafi Armati Siluranti (10th Torpedo Motorboat Flotilla, Decima MAS). The new force had a HQ, including a plans office and a weapons section. The surface assault boats and the training school (Lieutenant-Commander Giorgio Giobbe) were split from the human torpedoes and other underwater weapons (Lieutenant-Commander Junio Valerio Borghese), the captain of the Italian submarine Scirè. Decima MAS remained at La Spezia and an advanced base was set up in Augusta, Sicily.

The British code-breakers of the Government Code and Cypher School (GC & CS) alerted Admiral Andrew Cunningham the commander in chief of the Mediterranean Fleet before 17 December 1942, that its decodes of Italian messages encyphered on the Italian C 38m machine, showed that Supermarina, the Italian naval staff, had some interest in the port of Alexandria but without details. Torpedo nets were set up around the battleships HMS Valiant and Queen Elizabeth and other precautions were taken. On the day, Cunningham was told that an Italian reconnaissance aircraft had reported that Valiant and Queen Elizabeth were at their moorings and that the sea was calm, an unusual item to report. On 18 December GC & CS reported that the reconnaissance was urgent; Cunningham and his staff issued an alert at 10:25 a.m. that

Attacks on Alexandria by air, boat or human torpedo may be expected when calm weather prevails. Look-outs and patrols should be warned accordingly.

On 3 December, the submarine Scirè (Lieutenant Junio Valerio Borghese) of the Italian Regia Marina left the naval base of La Spezia carrying three manned torpedoes, nicknamed maiali (pigs). At the island of Leros in the Aegean Sea, the submarine secretly picked up six men of the Decima Flottiglia MAS, Lieutenant Commander Luigi Durand de la Penne and Sergeant-Major Emilio Bianchi (maiale nº 221), Captain Vincenzo Martellotta and Sergeant-Major Mario Marino (maiale nº 222) and Captain Antonio Marceglia and Lance Corporal Spartaco Schergat (maiale nº 223).

On the night of 18/19 December, 1.3 mi (1.1 nmi; 2.1 km) from the commercial (eastern) harbour of Alexandria, Scirè released the maiali at a depth of 49 ft (15 m) about 5 nmi (9.3 km; 5.8 mi) from the naval anchorage. The maiali reached the harbour and entered the naval base when the British opened the boom gate to let in three destroyers. The frogmen were shaken by the explosive charges being dropped in the harbour by patrol craft. The maiali crews found it comparatively easy to get over the torpedo nets around the battleships but attaching a charge to Valiant from its bilge keels was difficult and the crew dropped the explosive onto the sea bed about 15 ft (4.6 m) below the ship. Marceglia and Schergat, planting their bomb 5 ft (1.5 m) beneath the keel of Queen Elizabeth, found it much easier and suspended the charge from the bilge keels as planned. The maiali crew who attacked Valiant were discovered holding on to the mooring buoy but gave nothing away when questioned.