Operation Substance

Operation Substance was a British naval operation in July 1941 during the Second World War to escort Convoy GM 1, the first of the series from Gibraltar to Malta. The convoy, escorted by Force H, was attacked by Italian submarines, aircraft and MAS boats (Motoscafo armato silurante, motor torpedo boats).

Convoy
Port Chalmers carried 250 members of the Royal Artillery one light, one heavy anti-aircraft regiment and 30 field guns to strengthen the island against possible airborne assault. Medical personnel expected to be needed in the anticipated Siege of Malta were also embarked.

Force H included the battleship HMS Nelson (28), the battlecruiser HMS Renown (1916), the fast minelayer HMS Manxman (M70), the cruisers HMS Manchester (15), HMS Edinburgh (16) and HMS Arethusa (26) with eight destroyers and the aircraft carrier HMS Ark Royal (91) with 21 Fairey Fulmar fighters and ferrying seven Fairey Swordfish reinforcements to Malta.

Prelude
The Royal Navy observed a decrease in the intensity of Regia Aeronautica (Italian Royal Air Force) attacks as the stock of torpedoes at Sardinian airfields was nearly exhausted. The ships of convoy GM 1 sailed from the British Isles on 13 July 1941 as part of convoy WS (Winston Specials) 9C and arrived at Gibraltar on 20 July. Ships of the Mediterranean Fleet operating from Alexandria began making much radio traffic to divert attention from Gibraltar to preparations for a big operation in the eastern Mediterranean. Eight Allied submarines were deployed off Italian naval bases but Supermarina, the Italian naval headquarters, assumed the convoy was Ark Royal flying-off replacement aircraft to Malta and chose to remain in port. Leinster ran aground while leaving Gibraltar on 21 July and had to return to port. The Perla-class submarine ITALIAN SUBMARINE Diaspro found the convoy on 22 July and launched torpedoes which narrowly missed Renown and HMAS Nestor (G02).

Battle of 23 July
The convoy came under low level attack by nine Savoia-Marchetti SM.79 torpedo bombers coordinated with five CANT Z.1007 medium bombers. Four Fulmars met the torpedo planes head-on and shot one down before another SM.79 launched a torpedo, which hit Manchester, before also being shot down. Ark Royal launched seven more Fulmars which were unable to engage the high level bombers before they bombed, which failed to hit the merchant ships; three Fulmars were shot down. A later attack by two SM.79s sank HMS Fearless (H67) killing 35 of her crew. Another bombing attack near-missed HMS Firedrake (H79) causing damage requiring the destroyer to be towed back to Gibraltar. Bristol Beaufighters from Malta assisted Ark Royal Fulmars to defend the convoy.

HMS Cossack (F03) detected MAS boats 532 and 533 approaching the convoy after dark but was unable to prevent them from torpedoing SS Sydney Star at around 03:00 on 24 July. The merchant ship, carrying 484 army officers and men in addition to its normal crew, came to a dead stop as it took on water. Fearing that the ship's pumps were unable to cope with the damage, the captain requested evacuation of the troops. The Nestor came alongside and took on board approximately 500 men via gangplank and Jacob's ladder, leaving the captain and a skeleton crew on the Sydney Star. The captain later estimated that his ship had taken on 7000 LT of water. Nestor towed the damaged cargo ship to Malta, arriving at the Grand Harbour shortly after 08:00.

Aftermath
Seven empty ships sailed from Malta as convoy MG 1 on 23 July to be convoyed back to Gibraltar by Force H. One was damaged by an aircraft torpedo on the voyage west. Ark Royal lost six Fulmars defending convoy MG 1 and the Malta bound ships from Gibraltar and at least 12 Axis aircraft were destroyed by FAA fighters and the AA guns of the Royal Navy. The six merchant ships of Convoy GM 1 arrived in Malta on 24 July where they were observed by a CANT Z.506 reconnaissance seaplane, escorted by 42 Macchi C.200 fighters. Malta launched 22 Hawker Hurricane fighters, which shot down three of the escort without loss. The Battle of Grand Harbour an audacious attack on Grand Harbour by other MAS boats and manned torpedoes on the night of 25/26 July was thwarted by Ultra intelligence and ended in disaster for the Italians.