After entering service in the early part of the war in the Navy as a tanker, Sangamon was converted into an aircraft carrier.

On 7 December 1941, when the U.S. entered World War II, she was at Naval Station Argentia, Newfoundland, offloading her liquid cargo.

Sangamon and her three sister T3 conversions were considered very successful escort-carrier designs, larger and more stable than the smaller C3-derived Bogue class; additionally, they retained substantial oil bunkerage, useful in refueling destroyers in company.

Shakedown in Chesapeake Bay and off Bermuda followed a return to the yard for repair and improvements to her ventilation system, and on 25 October she sailed east with Task Force 34 (TF 34) to provide air cover for Operation Torch, the invasion of North Africa.

With Suwannee and Chenango, she provided protection for resupply convoys en route to Guadalcanal and for the assault forces moving on the Russell Islands.

Redesignated CVE-26 on 15 July 1943, Sangamon shifted her base of operations from Efate to Espiritu Santo in August, and, in September, she returned to the United States for an overhaul at Mare Island.

She got underway from the latter on 13 November, rendezvoused with Task Force 53 the next day, and on 20 October arrived in the Gilberts to support the assault on Tarawa Atoll.

Then, through 6 December, they were sent out on CAP and ASP missions to protect the escort carrier group and the target area.

It raged along the flight deck and flames beat up over the bridge, making ship control extremely difficult.

Temporary repairs were made at sea, and from 31 January to mid-February, Sangamon supported the assault and occupation of Kwajalein.

For the remainder of the month and into April she escorted that group as it operated north of the Admiralty Islands to refuel and resupply the fast carrier force after it had conducted strikes on the Palaus.

After the initial waves had landed, her planes shifted from combat support to bombing and strafing missions to destroy Japanese airfields on nearby Halmahera.

That group, composed of 18 escort carriers, was broken down into Task Units 77.4.1, 77.4.2, and 77.4.3 (TU 77.4.1, 77.4.2, and 77.4.3), and referred to as "Taffy 1, 2, and 3", respectively.

Early on 25 October, two flights took off: one toward the Mindanao Sea to locate and finish off Japanese survivors of the Battle of Surigao Strait, the other toward Leyte for CAP missions.

About an hour later, Sangamon received word that Taffy 3, 120 mi (190 km) to the north, had been attacked by the Japanese Center Force which had transited San Bernardino Strait during the night.

Within a half-hour, Sangamon's CAP flight had been diverted to Samar and she had launched another smaller group to further aid the attacked unit.

By 07:55, Japanese submarine I-56 (2) had joined the fight, and – as Santee's crew brought her fires under control – sent a torpedo into that luckless CVE.

Later in the morning, as the attacks fell off, she sent medical personnel to assist casualties of the damaged ships, then began bringing them aboard for treatment.

At mid-day, she suffered malfunctions in her steering gear, electric generators, and catapult, but repairs were completed in time for her to launch afternoon strikes as scheduled.

On 16 March she arrived at Ulithi where she was temporarily detached from her division to join TU 52.1.1, one of the escort carrier groups assigned to the initial assault phase of Operation Iceberg, the invasion of the Ryukyu Islands.

On 1 April, as the landings on the Hagushi beaches of Okinawa were taking place, she shifted to TU 52.1.3, thus rejoining CarDiv 22.

Through 8 April, however, she continued to launch supporting strikes and patrol groups from an area some 50 mi (80 km) south of Okinawa.

Detached on 12 April, she again provided air support for the forces fighting on Okinawa, then covered the occupation of Ie-shima.

On 22 April, eight fighters and four bombers of a dusk strike caught 25–30 enemy planes warming up on Nobara Field, central Miyako.

The escort carrier went into a hard left turn to avoid the enemy and to maneuver into a position to launch her aircraft.

At 19:25, another broke through the interceptor screen, ran into clouds to avoid anti-aircraft fire, then came out and, with increased speed, headed for Sangamon.

[2] The action of Sangamon swinging through the wind caused the flames and smoke to change direction, spreading the fires.

[2] Communication with other units had been regained; at first through the radio of Fullam, then by using a VHF channel in the sole remaining aircraft aboard.