'GM' (i) was the designation of British military convoys (with a numerical suffix) plying from Gibraltar to Malta, and as reciprocals of the 'MG' (i) series (21 July 1941/15 June 1942).

The first of the series was GM.1 of 20/24 July 1941 with the 8,049-ton British City of Pretoria, 7,440-ton British Deucalion, 10,893-ton British Durham, 11,076-ton British Melbourne Star, 20,043-ton British Orford, 8,535-ton British Port Chalmers, 17,702-ton British Reina del Pacifico, 19,761-ton British Scythia and 12,696-ton British Sydney Star. Of these, Britannic, Durban Castle, Orion and Strathaird became the RED.1 convoy at Gibraltar.

The ships reached Gibraltar as part of the the WS.9C convoy, which also included the with the 26,943-ton British Britannic, 17,388-ton British Durban Castle, 23,371-ton British Orion and 22,281-ton British Strathaird, which became the RED.1 The other ships became the core of the GM.1 supply convoy within 'Substance'.

(The designation GM.1 had already been used in September 1939 for liners from the Clyde river to Port Said and beyond.)

The the ships and forces from the UK for GM.1 had sailed from the Clyde in convoy WS.9C on 11 July, the merchant ships being the freighters City of Pretoria, Deucalion, Durham, Melbourne Star, Port Chalmers, Sydney Star and the small personnel ship Leinster bound for Malta plus the large personnel ship Pasteur with troops for Malta to be trans-shipped at Gibraltar. Accompanying the merchantmen were the light cruisers Arethusa and Manchester, cruiser minelayer Manxman, and destroyers Cossack, Lightning, Maori, Nestor and Sikh.

Pasteur left the convoy 17 July under escort of Manchester, Lighting and Nestor, which were soon joined by the escort destroyers Avon Vale, Eridge and Farndale despatched from Gibraltar. These ships reached Gibraltar on 19 July.

Leinster also detached on 17 July under escort of Arethusa, Cossack, Maori and Sikh, and reached Gibraltar early on 20 July. On sailing during the following day, Leinster ran aground and was unable to take in further part in the operation.

Manxman also detached from WS.9C and reached Gibraltar independently on 19 July.

'Substance' began on 21 July with the departure from Gibraltar of the oiler Brown Ranger escorted by the destroyer Beverley to provide refuelling within the Mediterranean for the destroyers escorting the convoy. The ships of the convoy from WS.9C passed through the Strait of Gibraltar at 01.45 on 21 July during a foggy, squally night escorted by the battleship Nelson, light cruiser Edinburgh, minelayer Manxman and destroyers Avon Vale, Eridge, Fury and Lightning, and were met by Arethusa, Manchester, Cossack, Maori, Nestor and Sikh, followed later on the same day by Vice Admiral Sir James Somerville’s Force 'H' with the battle-cruiser Renown, fleet carrier Ark Royal, light cruiser Hermione and destroyers Duncan, Faulknor, Fearless, Firedrake, Foresight, Forester and Foxhound. The destroyers of the convoy refuelled as required during 22 July from Brown Ranger, 10 ships in pairs, on completion of which the oiler and Beverley returned to Gibraltar, which they reached on 22 July.

On 23 July the MG.1A convoy (Breconshire, Amerika, Hoegh Hood, Settler, Svenør, Talabot and Thermopylae) departed Malta under escort of the destroyer Encounter. Svenør hit the breakwater on departure and had to return for repairs, the remaining ships steamed to the west to meet the oncoming warships.

Shadowing Axis aircraft reported Force 'H' and the convoy on 23 July and heavy air attacks developed at about 10.00 during which the cruiser Manchester and destroyer Fearless were torpedoed: the former was ordered back to Gibraltar accompanied by the escort destroyer Avon Vale, but the latter was beyond salvage and had to be sunk. Later in the day Firedrake was also hit while minesweeping ahead of the convoy and had to be towed toward Gibraltar by Eridge, and eventually reached that base under her own steam on 27 July escorted by Avon Vale and Eridge. Meanwhile Wishart, sent out from Gibraltar, had taken over the escort of Manchester and sent Avon Vale to reinforce Eridge.

In the dusk of 23 July the convoy now headed toward Sicily in a successful endeavour to avoid detection. In fact only two attacks, both by motor torpedo boats, were made on the convoy, although Sydney Star was hit in the second she remained afloat and continued her passage to Malta after some 500 troops onboard had been taken off by the destroyer Nestor; it is worthy of note that the Australian-manned Nestor already had crew and passengers of her own of 300 before this transfer.

Early on 24 July, Arethusa, Edinburgh and Manxman left the convoy and went on at high speed to Malta to land troops and stores, arriving in the island at noon followed four hours later by the convoy. The cruisers, plus Hermione which had brought in Sydney Star, departed that same evening to return to Gibraltar escorted by Cossack, Foxhound, Maori, Nestor and Sikh, leaving Farndale at Malta with defects.

The GM.2 convoy was the core of the 'Halberd' undertaking of 24/28 September 1941, the GM.3 convoy was the core of the 'Chieftain' undertaking on 16/16 November 1941, and the GM.4 convoy was the core of the 'Harpoon' undertaking of 5/15 June 1942.