After shakedown in the Caribbean, San Jacinto sailed, via the Panama Canal, San Diego, and Pearl Harbor, for the Pacific war zone. Arriving at Majuro, Marshall Islands, she became part of the growing might of Vice Admiral Marc A. Mitscher's Task Force 58/38, the fast carrier striking force of the Pacific Fleet. There, San Jacinto embarked Air Group 51, whose fighters and torpedo planes would be the ship's chief weapons in battle.
After providing search patrols to protect other carriers striking at Wake and Marcus Islands, San Jacinto, by 5 June 1944, was ready to participate in the largest fleet action since the battle of Midway, almost exactly two years before. On that day, Task Force 58 sortied from Majuro and headed toward the Marianas to conduct air strikes preparatory to American seizure of Saipan and to protect the invasion forces from enemy air and naval attack.
This American thrust triggered a strong Japanese reaction; on 19 June, the Japanese Fleet launched more than 400 planes against the invasion fleet and the covering carrier force. In the ensuing air battle, known to American pilots as the "Marianas Turkey Shoot," more than 300 enemy planes were shot down. While San Jacinto's planes were achieving their most one-sided victory of the war, her gunners helped to down the few attackers able to get near the American ships. Then, at dusk, Admiral Mitscher dispatched an all-carrier attack after the retreating enemy fleet. The night recovery of the returning planes was accomplished amid considerable confusion. Reportedly, a Japanese carrier plane attempted a landing approach on San Jacinto, only to be waved off by the landing signal officer because its hook wasn't down.
San Jacinto then participated in strikes against Rota and Guam and furnished combat air patrol (CAP) and anti-submarine patrol (ASP) for her task group. During these raids, a San Jacinto fighter pilot was shot down over Guam and spent 17 days in a life raft trying to attract attention and 16 nights hiding on the island.
After a refueling and replenishment stop at Eniwetok Atoll, San Jacinto joined in carrier strikes against the Palaus on 15 July. On 5 August, her targets were Chichi, Haha, and Iwo Jima. A brief stop at Eniwetok preceded dawn-to-dusk CAP and ASP duty while other carriers struck at Yap, Ulithi, Anguar, and Babelthuap, pinning down Japanese air forces while the Palaus were being assaulted on 15 September.
Following a replenishment stop at Manus, Admiralty Islands, San Jacinto joined in strikes against Okinawa and furnished photographic planes to get information necessary for future invasion plans. After refueling at sea, she once again supplied dawn-to-dusk air protection as other carriers sent strikes against Formosa, northern Luzon, and the Manila Bay area from 12 to 19 October. During operations on 17 October, a fighter plane made a very hard landing and inadvertently fired its machine guns into the ship's island structure killing two men, wounding 24, including her commanding officer, and causing considerable damage to radar. Despite this accident, San Jacinto remained battleworthy.
As American troops landed on Leyte in the central Philippines on 20 October, San Jacinto provided close air support. On 24 October, this mission was interrupted by news of the tri-pronged approach of the Japanese fleet which precipitated the largest fleet battle in naval history.
San Jacinto sent planes against the central force in the Sibuyan Sea, then raced north to launch strikes against the northern force, resulting in heavy damage to the Japanese carriers and surface combatants off Cape Engano. On 30 October, her fighters furnished air protection over Leyte while her guns shot down two planes attempting suicide attacks on the ship. After a pause at Ulithi, the carrier joined in attacks on the Manila Bay area; then took a side trip to Guam to exchange air groups, receiving Air Group 45. She received slight damage during a typhoon in December 1944.