When the Second World War began in September 1939, the ship was briefly assigned to the Home Fleet and conducted anti-submarine patrols in the Western Approaches.

Supported by several cruisers, the ship then blockaded Dakar and attempted to sink the Richelieu by exploding depth charges underneath her stern, as well as sending Fairey Swordfish torpedo bombers to attack her at night.

In February 1941, the ship supported Commonwealth forces in Italian Somaliland during the East African Campaign and did much the same two months later in the Persian Gulf during the Anglo-Iraqi War.

Hermes was berthed in Trincomalee on 8 April when a warning of an Indian Ocean raid by the Japanese fleet was received, and she sailed that day for the Maldives with no aircraft on board.

By this time, the uncertainty about the best configuration for an aircraft carrier had increased to the point that the Admiralty forbade the builder from working above the hangar deck without express permission.

The ship carried 2,000 long tons (2,000 t) of fuel oil which gave her a range of 4,480 nautical miles (8,300 km; 5,160 mi) at 16 knots (30 km/h; 18 mph).

[15] Hermes was laid down by Sir W. G. Armstrong-Whitworth and Company at Walker on the River Tyne on 15 January 1918[5] as the world's first purpose-designed aircraft carrier,[16] and was launched on 11 September 1919.

[18] Hermes conducted flying exercises with Eagle and the rest of the Mediterranean Fleet in early 1925 before she began a seven-week refit in Malta on 27 March, then sailed for Portsmouth where she arrived on 29 May after her aircraft had flown ashore.

Hermes returned to Hong Kong on 11 October and conducted routine training until she sailed to the naval base at Weihaiwei on 27 July 1927 to escape the summer heat.

[25] En route to Hong Kong, Hermes stopped at Bangkok, Siam, in March for four days and was inspected by King Rama VII.

While visiting Qinhuangdao in July, one of her Fairey IIIF seaplanes made a forced landing outside the port; the Italian destroyer Muggia rescued the pilot and towed the aircraft back to the carrier.

[26] On 28 January 1930, Hermes transported the British Minister to China, Sir Miles Lampson, to Nanjing for talks with the Chinese Government over the Japanese invasion of Manchuria and she remained there until she sailed downriver to Shanghai on 2 March.

Eight of the submarine's crewmen managed to escape through the forward torpedo hatch, but only six of those reached the surface where they were picked up and treated in Hermes's sickbay; two of those six subsequently died.

Hermes received a distress message on 3 November from a Japanese merchantman, SS Ryinjin Maru, that had run aground on the Tan Rocks near the Chinese mainland at the mouth of the Taiwan Strait.

After a short refit, the carrier, escorted by the destroyer Whitehall, made a brief visit to Amoy in late April before sailing for Weihaiwei where she stayed until 17 September.

She reached Sheerness on 22 July, but the ship was transferred shortly afterwards to Chatham Dockyard and opened to the public during Navy Week in early August.

There she remained until 12 September when the Admiralty decided to transfer her to Singapore where she was closer to East Africa in case a military response to the Italian invasion of Ethiopia was deemed necessary.

[33] The ship's aircraft were detailed to search for the missing Lady Southern Cross of Sir Charles Kingsford Smith when it failed to arrive at Singapore on 8 November during an attempt to set a new speed record between Britain and Australia.

For most of January 1937, the carrier, accompanied by the heavy cruiser Dorsetshire and the destroyers Duncan and Diana, toured the Dutch East Indies.

On 18 September, the day after the fleet carrier Courageous was sunk on one such patrol, Hermes located a submarine, but attacks by her escorting destroyers, Isis and Imogen, were ineffective.

On the night of 7/8 July, a boat from Hermes attempted to drop four depth charges underneath the French battleship Richelieu's stern in conjunction with a torpedo attack by the Swordfish of 814 Squadron.

While returning to Freetown after the attack, Hermes accidentally rammed the armed merchant cruiser HMS Corfu during a rainstorm in the dark on 10 July.

They were pulled apart by a combination of the carrier's turbines at full speed astern and blowing of ballast tanks on board Corfu to lighten that ship forward.

They mostly operated from Saint Helena during the month and were later joined by the armed merchant cruiser Pretoria Castle to search for the pocket battleship Admiral Scheer, without success.

The force sailed for Simonstown on 31 December and Hermes was dispatched to search off the South African coast for Vichy French blockade runners.

On 4 February, the ship headed north to rendezvous with the heavy cruisers Shropshire and Hawkins to blockade the Somali port of Kismayo which was under siege by Commonwealth forces.

[38] On 22 February, the carrier was one of the ships tasked to search for Admiral Scheer after she was spotted by an aircraft from the light cruiser Glasgow, but the pocket battleship successfully broke contact.

She was sent to the Persian Gulf in April to support British operations in Basra, Iraq, and remained there until mid-June when she returned to patrolling the Indian Ocean between Ceylon and the Seychelles Islands.

[40] After the raid on Colombo by the Japanese aircraft carriers on 5 April, Hermes and Vampire were sent to Trincomalee to prepare for Operation Ironclad, the British invasion of Madagascar, and 814 Squadron was sent ashore.

[42] The British intercepted the spot report and ordered the ships to return to Trincomalee with the utmost dispatch and attempted to provide fighter cover for them.