She was completed during World War II and provided air cover over the amphibious landing at Salerno, Italy, in September 1943.

She spent most of the war ferrying aircraft, troops, stores and equipment in support of Commonwealth operations in Korea.

Admiral Reginald Henderson, Controller of the Navy was instrumental for gaining approval for the ship and ensuring that she had a complete flight deck that would allow her to land, service and launch aircraft on active operations.

[6] The ship carried 3,000 long tons (3,000 t) of fuel oil which gave her a range of 7,000 nautical miles (13,000 km; 8,100 mi) at 13.5 knots (25.0 km/h; 15.5 mph).

[18] In late May, Unicorn escorted Convoy MKF 15 to Gibraltar while carrying a number of Royal Air Force Bristol Beaufighters that she off-loaded there.

Together with the aircraft carrier Illustrious, the ship made a sweep towards the Norwegian coast as part of Operation Governor, a diversion for the Allied landings in Sicily in early July.

[20] Unicorn was assigned to Force V, a flotilla of British carriers, commanded by Admiral Philip Vian, intended to provide air cover to Operation Avalanche, the Allied landings at Salerno.

[21] Unicorn joined the escort carriers of Force V in August at Gibraltar before they moved forward to the Central Mediterranean for intensive training prior to the commencement of the amphibious landing on 9 September.

[21] The ship returned to the UK on 20 September with a full load of damaged Seafires, in addition to her own aircraft, that were off-loaded at Glasgow to be repaired.

[24] At the end of December 1943, Unicorn joined Illustrious, the battlecruiser Renown and the battleships Queen Elizabeth and Valiant, the other reinforcements for the Eastern Fleet.

[26] The ship delivered a consignment of aircraft to Royal Navy Air Station Cochin, India, on 27 January 1944 before arriving at Trincomalee, Ceylon on 2 February.

On 7 November, 817 Squadron flew aboard to provide anti-submarine protection with its Fairey Barracudas[27] as Unicorn was ordered to Durban, South Africa.

There she was to be modified with separate workshops and additional equipment to accommodate American engines which used different screw threads and electrical fittings.

The ship loaded 82 aircraft and 120 engines later in the month for transport to Australia, emptying the available stocks of the Eastern Fleet, and departed for Sydney on 29 January.

The ship arrived at San Pedro Bay, Philippines on 27 March which was to serve as the BPF's intermediate replenishment base while it supported Operation Iceberg.

[29] The BPF was tasked to attack Japanese airfields in the Sakishima Islands and Formosa before and during the early stages of the invasion of Okinawa.

The ship began to ferry aircraft, equipment and men back to Australia after the surrender, a task which ended on 6 November, when she arrived at Sydney.

When the Korean War broke out in June 1950, the ship was disembarking aircraft, equipment and her maintenance personnel at RAF Sembawang, Singapore in preparation to return home and then to reserve.

[32] Unicorn resumed her duties in December, carrying about 400 troops in addition to the usual aircraft, stores and equipment.

Whilst transiting the Shimonoseki Strait on 2 October, she destroyed the overhead power cables stretching between Honshu and Kyushu as they were sagging lower than normal due to a heavy snowfall.

On 21 November, Unicorn and the carrier Warrior exchanged crews at Singapore and the ship began a refit shortly afterwards.

She arrived back at Singapore on 27 July to load more replacement aircraft, including Meteors, and sailed on 9 August for Japan.

During September, Unicorn borrowed four of Ocean's Hawker Sea Fury fighters to fly combat air patrols over the fleet whilst the latter ship conducted strike operations.

She was docked for maintenance in October, and embarked the First Sea Lord, Admiral Rhoderick McGrigor and the Commander-in-Chief, Far East Station for a tour of Commonwealth forces in Japan.

On 26 July, en route for Japan, Unicorn received a distress call from SS Inchkilda south of the Wuqiu region in the Taiwan Strait, saying that she was under attack by pirates - 3 gunboats of the ROC Anti-Communist National Salvation Army (ACNSA).

This reconstruction would have begun in July 1954, but the entire scheme was cancelled in November 1952 because providing existing carriers with angled flight decks was much more important.