'Chieftain' was a British naval undertaking in support of 'Crusader' (i) and based on the movement of the GM.3 convoy as a diversion in the western Mediterranean (16/17 November 1941).

The operation represented an attempt to draw Axis air strength toward the western end of the Mediterranean by despatching a decoy convoy into the Mediterranean from Gibraltar. The GM.3 convoy comprised the 3,386-ton Baron Newlands, 3,319-ton Blair Atholl, 1,886-ton Cisneros, 2,870-ton Ottinge and 1,575-ton Shona, together with the fleet oiler Brown Ranger, escorted by the destroyer Wild Swan, the sloop Deptford, and the corvettes Convolvulus, Rhododendron and Samphire.

The convoy departed Gibraltar during the evening of 16 November, and the intention was that each merchant ship should break off and return independently under cover of darkness, while the naval vessels remained at sea for two days carrying out an anti-submarine sweep.

The corvette Marigold, which sailed late as a result of the time it took to remedy an engine problem, located and sank Oberleutnant Hans Ey’s U-433.

To further the deception that the convoy was bound for Malta, Force 'K' departed the island on 18 November with the light cruiser Aurora, the light anti-aircraft cruiser Penelope, and the destroyers Lance and Lively. The ships arrived back at Malta during the night of 18/19 November.

Over the same period, the battleships Barham, Queen Elizabeth and Valiant, the light cruiser Galatea, the light anti-aircraft cruisers Euryalus and Naiad, the destroyers Decoy, Jackal, Jervis, Kimberley, Kingston, Kipling, Napier and Nizam, and the escort destroyers Avon Vale and Eridge of Admiral Sir Andrew Cunningham’s Mediterranean Fleet departed Alexandria in 'ME4', and then turned back after dark to arrive in Alexandria during the morning of 19 November.

Euryalus, Naiad, Jackal and Kipling had been detached late on 18 November, and bombarded the Axis defences at Halfaya before turning back to Alexandria.