'M.42' was an Italian convoy operation from Italy to North Africa leading to the 1^st Battle of Sirte (16/17 December 1941).

The battle was fought between British and Italian warships in an area to the north of the Gulf of Sirte and to the west of Malta in the immediate aftermath of the abortive 'M.41' convoy. On 16 December, the four-ship Italian 'M.41' convoy, redesignated as 'M.42' and comprising the 5,324-ton Italian Monginevro, 6,142-ton Napoli and 6,339-ton Vettor Pisani and the 4,768-ton German Ankara, departed Taranto and linked with its escort. The close escort comprised the destroyers Ugolino Vivaldi, Antonio da Noli, Nicoloso da Recco, Lanzerotto Malocello, Emanuele Pessagno, Nicolo Zeno and Saetta, together with the torpedo boat Pegaso.

By the time they reached Sicily, the convoy and its close escort were also accompanied by Ammiraglio di Squadra Carlo Bergamini’s close cover force, comprising the battleship Caio Duilio, Ammiraglio di Squadra Conte Raffaele de Courten’s 7a Divisione Incrociatori (the light cruisers Emanuele Filiberto Duca d’Aosta, Muzio Attendolo and Raimondo Montecuccoli) and the destroyers Aviere, Ascari and Camicia Nera. A third group, Ammiraglio di Armata Angelo Iachino’s distant cover force, comprised the battleships Littorio, Andrea Doria and Giulio Cesare, Ammiraglio di Divisione Angelo Parona’s 3a Divisione Incrociatori (heavy cruisers Gorizia and Trento) and the destroyers Granatiere, Bersagliere, Fuciliere, Alpino, Corazziere, Carabiniere, Antoniotto Usodimare, Maestrale, Vincenzo Oriani and Alfredo Gioberti.

Some measure of the importance of the 'M.42' convoy can be seen in the fact that 30 Italian warships were used to escort just four cargo ships. The two British groups mentioned in 'M.41' were also still at at sea and steaming toward each other, and the opposing forces were destined to cross each others' tracks to the east of Malta on 18 December. Although the resulting combat between the convoy’s escorts and their British attackers was indecisive, Captain W. G. Agnew’s Malta-based Force 'K' inadvertently entered an Italian minefield after the battle and suffered losses which ended its existence as an effective fighting force.

Late in 1941 Lieutenant General N. M. Ritchie’s British 8^th Army in North Africa had driven back the German and Italian forces spearheaded by Generaloberst Erwin Rommel’s Panzergruppe 'Afrika' and had taken Benghazi on the eastern side of the Gulf of Sirte. This pushed the front line of the North African campaign well west of the position in had occupied only a few weeks earlier, and opened the possibility of new bases for Air Vice Marshal A. Coningham’s Western Desert Air Force to operate against the Italian shipping that provided the only surface link between Italy and the Axis forces fighting in North Africa.

Even as the British and commonwealth forces were advancing across Cyrenaica toward the Gulf of Sirte, the Italians were planning the 'M.42' convoy to reinforce and resupply the Axis forces in North Africa. The convoy of four merchantmen left Naples on 16 December, and was joined by its close escort on passage to the south along the west coast of the Italian mainland. An air reconnaissance of Malta then reported, quite erroneously, that there were two British battleships in Valletta harbour, and this persuaded the Italian navy to increase the strength of the convoy’s escort. By the time the convoy neared Sicily, it had been joined by the close covering force under the command of de Courten. Farther off was the distant covering force under the command of Parona.

The opposing British forces were considerably smaller, and comprised two groups totalling 20 somewhat lighter warships. Overall command was vested in Rear Admiral P. L. Vian, who led Force 'B' comprising the light anti-aircraft cruisers Carlisle, Euryalus and Naiad, and the 14^th Destroyer Flotilla with Jervis, Kimberley, Kingston, Kipling, and Australian Nizam, Havock, Hasty and Decoy. Agnew’s Force 'K' comprised the light cruisers Aurora, Penelope and Neptune, and the 4^th Destroyer Flotilla with Sikh, Maori, Legion and Free Dutch Isaac Sweers. Another two destroyers, Jaguar and Kandahar, provided close escort for Breconshire running supplies into Malta.

On 17 December an Italian reconnaissance aeroplane spotted a British naval force near Sidi Barrani, apparently proceeding from Alexandria to intercept the Italian convoy. Among this defensive force was a battleship, persuading the Italian naval command that three British battleships were in the general area. In fact, the ships in question were actually escorting a British convoy to Malta, and the 'battleship' was later discovered to be Breconshire, disguised with painted-on guns.

Iachino ordered the Italian forces to close and engage, but believing that the ships off the North African coast were a British task force aiming to intercept his convoy, instead of pressing the attack as quickly as he could, he manoeuvred slowly, apparently in order to keep the British away from the Italian convoy. Admiral Sir Andrew Cunningham, commanding the Mediterranean Fleet, had instructed Vian to avoid combat, so with the British pulling back and the Italians pursuing with caution, the British were able to avoid any engagement. Just after the fall of night, a Luftwaffe attack on the British ships elicited a strong defence from the warships' anti-aircraft guns, allowing the Italians at last to spot them.

Iachino closed with the distant covering force and opened fire at a range of some 35,000 yards (32000 m), which was well out of the capability of the British warships' ability to respond. Vian immediately ordered his vessels to make smoke, and attempted to retreat. Lacking radar, and conscious of the defeat this had inflicted on them in the Battle of Cape Matapan during their 'Gaudo' operation, the Italians justifiably wished to avoid night combat. Expecting an attack, the Italians engaged the British ships for only 15 minutes before disengaging and turning west to protect the 'M.42' convoy. Only two British destroyers suffered the effects of Italian gunfire: Kipling received a near-miss from a 8-in (203-mm) projectile, presumably fired by Gorizia, and had one man killed; and Nizam was also the subject of near-misses from the Italian destroyer Maestrale.

Both convoys managed to reach their ports, an important success for the Italians, who had repeatedly suffered heavy losses in their Libya-bound convoys. Only at this stages realising that the Italians were also escorting a convoy, Force 'K' tried to effect an interception of the Italian ships on their passage back to Italy. On the night of 19 December Force 'K' ran into an extensive Italian minefield about 15 miles (24 km) off Tripoli. Neptune struck four mines and sank, and Kandahar also struck a mine and suffered damage so severe that the ship was perforce scuttled during the following day. Aurora and Penelope were also badly damaged, but were able to return to Malta. About 950 British seamen, many of them New Zealanders from Neptune, lost their lives in the disaster.

Force 'K', which had been an active threat to Axis shipping on the run between Italy and Libya through much of 1941, had effectively ceased to exist. This situation, along with the temporary incapacitation of the battleships Valiant and Queen Elizabeth to Italian manned torpedo attack in Alexandria, occasioned something of a strategic change of fortune in favour of the Italians and Germans in the central Mediterranean for the few months which followed.