She was powered with two Skinner Unaflow reciprocating steam engines, which drove two shafts, providing 9,000 horsepower (6,700 kW), thus enabling her to make 19 knots (35 km/h; 22 mph).

[1][9] Upon being commissioned, Fanshaw Bay took on armaments at Port Townsend, Washington on 31 December, and proceeded on a shakedown cruise down the West Coast.

[9] On 29 May, she sortied from Pearl Harbor, bound for Eniwetok Atoll, where she acted as the flagship of Task Group 52.14, which was assigned to support the upcoming Mariana and Palau Islands campaign.

On 15 June, at 17:15 in the late afternoon, the officers of Fanshaw Bay received a report of five Japanese aircraft proceeding towards her task group 71 mi (114 km) to her southwest.

Fortunately for the carrier, the Japanese plane approaching from the starboard bow, perhaps disrupted by the anti-aircraft fire, dropped its torpedo at a slight turn.

[9] On 17 June, one of Fanshaw Bay's torpedo bombers conducting antisubmarine patrols crashed shortly after takeoff, veering port into the sea.

[9] However, at 18:52, a Japanese bomber made a run for Fanshaw Bay, dropping a bomb (believed to be 250 lb (110 kg)) as it flew about 1,500 ft (460 m) above the carrier.

Nonetheless, the blast had enough force to rupture a fire main, sever electrical cables, and to even eject depth charges from the bomb bays of the Avengers stored within the hangar deck.

[13] Bogan, continuously frustrated by the progress of damage control, later complained in a 1969 interview that Fanshaw Bay was "the worst ship [he’d] ever seen in any Navy" and that "the entire complement was incompetent.

[9] Upon finishing her repairs, Fanshaw Bay continued acting as the flagship of Carrier Division 25, now under the command of Rear Admiral Clifton A. F. Sprague.

At the time, her task group was operating 35 mi (56 km) to the north of the island, when the Japanese submarine Ro-41 fired a spread of torpedoes towards the escort carriers.

This prompted Admiral Soemu Toyoda to launch Shō-Gō 1, a gambit to defend Japan's access to the oil fields of Southeast Asia.

On 18 and 19 October, Taffy 3 conducted strikes against Japanese bases located within Cebu, Negros, and Panay, destroying a total of thirty-eight planes, and damaging twenty-eight more.

Taffy 3, the northmost task group, would bear the brunt of Vice Admiral Takeo Kurita's Center Force as it swung through the San Bernardino Strait.

[18][9] On the early morning of 25 October, Kurita's Center Force had already crossed the San Bernardino Strait unmolested, and was entering the open waters of Leyte Gulf.

Although World War II era surface radar was notoriously faulty, the speed and course of the spotted blip was consistent with the course set by the Center Force.

By the time of the attack, Fanshaw Bay therefore only had twelve aircraft on hand, none of which were equipped to deal with heavily armed surface warships.

[20][9] Upon coming to an understanding of the severity of the situation, Sprague ordered Taffy 3 to steam eastward, in hopes of being shielded by a passing rain squall.

[21] Sprague also radioed for assistance from Vice Admiral Jesse B. Oldendorf, the commander of Task Group 77.2, which had just defeated the Southern Force in the Battle of Surigao Strait.

Unfortunately for Sprague, Oldendorf was at least three hours sail away, Task Group 77.2 was scattered over an immense distance because of the previous night's battle, and it was low on both fuel and ammunition.

The Japanese were firing dye-marked shells to gauge their aim, and the escort carriers were, much to the concern of their command, straddled in plumes of colored water.

Fortunately for Fanshaw Bay's crew, as the shells slowly creeped up to her stern, she happened across a passing rain squall at 7:03, reducing visibility to just 0.5 mi (0.80 km).

[23] At the same time that Fanshaw Bay was being harried by shells, the twelve aircraft that she had launched, joined by four fighters which had been on patrol, commenced attacks against the leading Japanese ships.

Fortunately for her crew, Admiral Kurita, discouraged by the dogged defense of Taffy 3 and his losses, harried by constant air attacks, and believing that he was facing an equal or perhaps a superior force, was convinced to withdraw.

In addition, Gambier Bay was severely damaged and sunk as a result of Japanese naval gunfire, with her survivors being left behind by the beleaguered task force.

[8] Fanshaw Bay remained on station off of Okinawa for sixty-nine consecutive days, and her air contingent flew 2,089 sorties in the battle, claiming five Japanese planes.

Fanshaw Bay, along with three other escort carriers, provided an aerial screen for the minesweepers, and launched strikes against targets situated around the mouth of the Yangtze River on 28 July.

On 30 July, she withdrew from the operations, having assisted the minesweepers in clearing 404 mines over 7,300 sq mi (19,000 km2), with no loss in ships, despite the occasional Japanese submarine or plane.

She cruised around the Pacific, making stops and returning U.S. servicemen back to the mainland, sailing a total of 23,500 mi (37,800 km) along the way, and with an average of 1,400 passengers on-board during each journey.

She then made a trip to Japan, arriving at Tokyo Bay on 28 November, returning to the West Coast on 18 December, where she was discharged from the "Magic Carpet" fleet.