'Substance' was the British GM.1 reinforcement convoy to Malta and the recovery of empty ships in the reciprocal MG.1 (21/27 July 1941).

At the time in question Malta’s garrison was in dire need of reinforcements and supplies, but as no convoy could be passed westward through the Mediterranean from Alexandria because of the current strength of Italian naval strength and Axis air power, it was decided to make the attempt with an eastward convoy from the UK via Gibraltar.

The British plan was that the 4,302-ton troopship Leinster and six cargo-laden British merchant vessels, in the form of the 8,049-ton City of Pretoria, 7,740-ton Deucalion, 10,893-ton Durham, 12,806-ton Melbourne Star, 8,535-ton Port Chalmers and 12,696-ton Sydney Star, should make the passage through the western basin of the Mediterranean Sea to Malta while a number of empty ships, in the form of the 9,776-ton commissioned transport Breconshire, 10,218-ton British Amerika, 6,202-ton British Settler, 6,798-ton Norwegian Talabot, 6,655-ton Norwegian Thermopylae, 9,351-ton Norwegian tanker Hoegh Hood and 7,616-ton Norwegian tanker Svenor, escaped from the island to Gibraltar.

The significance of the operation is attested by the fact that Vice Admiral Sir James Somerville’s Gibraltar-based Force 'H' was temporarily reinforced by a detachment of Admiral Sir John Tovey’s Home Fleet in the form of the battleship Nelson and the light cruisers Arethusa, Edinburgh and Manchester.

At that time designated as WS.9C, the convoy departed the Clyde river on 11 July, and in addition to the vessels mentioned above included the 29,253-ton large personnel transport Pasteur with troops for Malta, who were to be trans-shipped at Gibraltar. Accompanying the merchant vessels were the light cruisers Arethusa and Manchester, the cruiser minelayer Manxman and the destroyers Cossack, Lightning, Maori, Nestor and Sikh. Pasteur left the convoy on 17 July, escorted by Manchester, Lightning and Nestor, supplemented by the escort destroyers Avon Vale, Eridge and Farndale sent out from Gibraltar, and reached Gibraltar on 19 July. Leinster was also detached on 17 July, escorted by Arethusa, Cossack, Maori and Sikh, and reached Gibraltar early in the morning of 20 July.

Departing on the following day, Leinster ran aground and was unable to take any further part in the operation: some 3,200 of the 5,000 troops and airmen on board were transferred to other ships, but the balance of 1,800 men was left for 'Style' (i), undertaken a few days later. Manxman was also detached from the WS.9C convoy and reached Gibraltar on 19 July.

These arrivals allowed the 'Substance' operation proper to begin on 21 July. The British plan was for Admiral Sir Andrew Cunningham’s Mediterranean Fleet to sortie from Alexandria in order to deal with the Italian fleet should the latter emerge from Taranto, Palermo and Messina, for a patrol group of eight submarines to lurk on the likely approach routes of any Italian surface forces, and for the convoy to head to the east under escort of Force 'H' which, as noted above, had been significantly reinforced for this undertaking and would turn back in the Sicilian Narrows, leaving the convoy to proceed to Malta under the close escort of Rear Admiral E. N. Syfret’s force (comprising the light cruisers Arethusa, Edinburgh and Manchester, the cruiser minelayer Manxman, the destroyers Cossack, Encounter, Fearless, Firedrake, Foxhound, Maori and Australian Nestor, and the escort destroyers Eridge and Farndale) as the ships from Malta escaped to the west.

The operation proper began on 21 July with the departure of the oiler Brown Ranger, escorted by the destroyer Beverley, to provide refuelling within the Mediterranean for the destroyers escorting the convoy. The ships from the WS.9C convoy passed through the Strait of Gibraltar at 01.45 on 21 July during a squally night of low visibility under escort of the battleship Nelson, light cruiser Edinburgh, cruiser minelayer Manxman, and destroyers and escort destroyers Avon Vale, Eridge, Farndale, Fury and Lightning, to be met by Arethusa, Manchester, Cossack, Maori, Nestor and Sikh.

Later in the day there followed Force 'H', in the form of the battle-cruiser Renown, the fleet carrier Ark Royal, the light anti-aircraft cruiser Hermione and the destroyers Duncan, Faulknor, Fearless, Firedrake, Foresight, Forester and Foxhound. The convoy’s destroyers fuelled as required during 22 July from Brown Ranger, the ships taking on oil fuel in pairs, and on completion of this task the oiler and Beverley returned to Gibraltar, where they arrived on 23 July.

On this day the MG.1A convoy (Breconshire, Amerika, Hoegh Hood, Settler, Svenor, Talabot and Thermopylae) departed Malta escorted by the destroyer Encounter. Svenor hit the breakwater on departure and had to return for repairs, the remaining ships steaming to the west to meet the oncoming warships.

Axis reconnaissance aircraft reported Force 'H' and the convoy on 23 July, and heavy air attacks developed at about 10.00. The operation had proceeded without undue incident up to this time, but with the convoy now to the south of Sardinia it came under heavy air attack. Despite the efforts of the fighters flown off Ark Royal, the first casualties were Manchester, which was so heavily damaged by a torpedo that she had to return to Gibraltar accompanied by the escort destroyer Avon Vale, and the destroyer Fearless, which had eventually to be sunk by the British. The vital storeships were undamaged, however, and reached the Skerki Channel at 17.00 for the final dash to Malta after the main strength of Force 'H' had turned back. Later in the same 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 Syfret turned to the north after the fall of night, deciding that the longer passage would be more than balanced by freedom from Axis minefields and the possibility of losing shadowing aircraft in the dark, and the commander was proved right in both respects. In fact only two attacks, by Italian motor torpedo boats, were made on the convoy, and 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 Australian destroyer Nestor: the destroyer already had her own crew and passengers, totalling 300 men, before this transfer.

Early on 24 July Arethusa, Edinburgh and Manxman left the convoy for a high-speed dash to Malta to land their troops and stores, arriving in the island at 12.00. The convoy reached the island four hours later. The cruisers, plus Hermione which brought in the battered Sydney Star, sailed that evening to return to Gibraltar escorted by Cossack, Foxhound, Maori, Nestor and Sikh, leaving Farndale at Malta with mechanical problems. Finally, Somerville again headed for Malta to provide air cover over Syfret’s returning force, and by 27 July Force 'H' was safely back at Gibraltar.