The Japanese did not react to the operation as the Eastern Fleet was not seen as a serious threat and their forces in the area were being preserved for use against an expected major American offensive in the Central Pacific.

[3] At the Cairo Conference held during November 1943, the Allied leadership agreed that "the main effort against Japan should be made in the Pacific", and that the Indian Ocean would be a subsidiary theatre.

[4] In January 1944 the Admiralty, the British Government institution responsible for administering the Royal Navy, decided to substantially reinforce the Eastern Fleet.

[5] The reinforcements which were scheduled to arrive over the next four months comprised 146 warships, and included three battleships, two aircraft carriers, fourteen cruisers and large numbers of destroyers and other escort vessels.

[2] Shortages of destroyers hindered the fleet's ability to conduct offensive operations until April, however, as priority needed to be given to escorting convoys.

This was done to evacuate the fleet's bases in the central Pacific, which were now vulnerable to American attacks, and concentrate it at a location with good naval repair facilities and ready access to fuel.

[7] The United States Navy also agreed to temporarily transfer the aircraft carrier USS Saratoga and three destroyers from the Pacific to augment the Eastern Fleet; this was done so that the British did not have to free up reinforcements for the Eastern Fleet by cancelling the planned Operation Tungsten carrier raid on the German battleship Tirpitz in Norway.

[11] The IJN's 9th Base Force was the main unit stationed at Sabang, and was commanded by Rear Admiral Hirose Sueto from February 1944.

[13] In late March the main body of the Eastern Fleet, including Illustrious, Renown, Queen Elizabeth and Valiant, sortied into the Indian Ocean.

The main goals of what was designated Operation Diplomat were to search for Japanese ships following an unsuccessful cruiser raid and link up with Saratoga.

[10] Intelligence gained from breaking German and Japanese codes contributed to the planning for Operation Cockpit by allowing the Allies to track the locations of enemy warships and air units in the region.

The IJN was aware that the fleet was too weak to pose a significant threat, and were preserving their forces, including the aircraft in southern Malaya, to contest the American advance through the central Pacific.

[17] The attack force sailed from the Eastern Fleet's main base at Trincomalee on 16 April, and was led personally by Somerville from Queen Elizabeth.

[24] After an uneventful journey, and without being detected by the Japanese, the Allied force arrived at the carriers' flying off point 100 miles (160 km) south-west of Sabang in the early hours of 19 April.

The strike force began to be launched at 5:30 am; Illustrious dispatched 17 Barracudas and 13 Corsairs and Saratoga 24 Hellcats, 18 Dauntlesses and 11 Avengers.

Anti-aircraft batteries began firing on the Allied aircraft after the attack had commenced, and no Japanese fighters were encountered in the air.

[18][27][28] Clifton led a group of fighter aircraft which drove off a Japanese torpedo boat that was threatening the submarine during the rescue.

During a rain squall in the afternoon of 20 April Renown mistook the Australian destroyer HMAS Nepal for a Japanese vessel and briefly engaged it with her secondary armament.

[21][32] Shortly after the attack force reached Ceylon, Saratoga received orders to return to the United States for a refit.

[33][34] The Eastern Fleet made several other carrier raids during 1944, including a second attack on Sabang on 25 July designated Operation Crimson.