During the spring and summer, the need for auxiliary carriers, later called escort carriers, increased. Work on Sangamon, three other Cimarron class oilers, and twenty C-3 merchant hulls was continued and sped up. In August, Sangamon, the first of her class of escort aircraft carriers, was ready. Her conversion had added a flight deck long and wide, elevators, a hangar deck, a catapult, sonar gear, aircraft ordnance magazines, work shops, and stowage space for aviation spares. Her accommodations had been enlarged to house her increased complement and embarked aviation personnel, and her armament had been changed to 2 × 5 inch, 8 × 40 millimeter, and 12 × 20 millimeter guns to increase her anti-aircraft defense. On 20 August, she was redesignated ACV-26; and, five days later, she was recommissioned, with Captain C. W. Wieber in command.
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. There she received more modern equipment for her flight deck and a Combat information center.
On 19 October, she departed San Diego with VC-37 embarked and sailed for Espiritu Santo. She got underway from the latter on 13 November; rendezvoused with Task Force 53 (TF 53) the next day; and on October 20, arrived in the Gilberts to support the assault on Tarawa. During the first two days of this operation, her planes struck enemy positions on the island. 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. The former oiler was turned out of the wind, so that the fire could be fought. By 16:59, it was under control. Seven of the crew died in those 8 minutes. Seven others were seriously injured, and of the 15 who jumped over the side to escape the flames, 13 were picked up, two were missing.
On 15 March, the CVE got underway again. Departing Hawaii, she rendezvoused with Task Group 50.15 (TG 50.15), the fast carrier force support group, on March 26. For the remainder of the month and into April she escorted that group as it operated north of the Admiralties to refuel and resupply the fast carrier force after it had conducted strikes on the Palaus. In early April, Sangamon retired to Espiritu Santo and at mid-month, sailed for New Guinea. Briefly attached to the United States 7th Fleet, she covered the landing at Aitape from 22–24 April; retired to Manus for two days; then returned to the Aitape area where she conducted patrols until 5 May.
Sangamon then returned to Espiritu Santo, whence she departed on 19 May. Rehearsals for the Marianas campaign followed; and on 2 June, she sailed for the Marshalls. Rendezvousing with TF 53 en route, she covered that force to Kwajalein, then to the Mariana Islands. From 17–20 June, she guarded the force as it steamed to the east of Saipan as a backup force for TF 52, which was then engaged in the assault on, and the occupation of, the island.
After the Battle of the Philippine Sea, Sangamon was detached from TF 53. On 21 June, she joined TF 52 and, into July, conducted operations in support of the occupation of Saipan. On 4 July, she steamed for Eniwetok; arrived on 7 July, and sortied again on 10 July. From 13 July to 1 August, she covered the bombardment groups engaged in the capture of Guam. On 4 August, she returned to Eniwetok, whence, on 9 August, she proceeded to Manus where she was anchored for almost a month.
On 9 September 1944, Sangamon departed Seeadler Harbor and steamed for Morotai. There, from 15–27 September, she again covered Allied assault forces. After the initial waves had landed, her planes shifted from combat support to bombing and strafing missions to destroy Japanese airfields on nearby Halmahera.
Prior to 20 October landings on Leyte, Sangamon launched regular flights in support of the advance units of the invasion force and sent strikes against Leyte and Visayan airfields. On the 20th, her planes covered the landing forces and the ships in the transport areas. That day, she also came under enemy air attack and took a hit at the main deck level. The bomb, dropped by a "Zeke", tore a two by six foot section of plating loose, then fell into the sea and exploded some away from the "jeep" carrier.
Enemy airfields again became Sangamon's primary targets in the days immediately following the landings. On 24 October, however, her planes fought off waves of Japanese aircraft over the landing area. 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", 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. Soon thereafter, however, at about 07:40, as "Taffy 1" planes were being recovered, rearmed, and launched, the unit became the target of the first strike of Kamikaze. took the first hit, and as her flight and hangar decks blazed, Suwannee was attacked. Antiaircraft fire from that CVE scored on the planes, which then dived toward Sangamon. A shell from Suwannee finished one plane only from Sangamon. By 07:55, a Japanese submarine, I-56, had joined the fight, and, as Santee's crew brought her fires under control, sent a torpedo into that luckless CVE. Minutes later, Suwannee was crashed by a "Zeke" forward of the after elevator.
During the intense fighting, several of Sangamon's crew were injured and one was killed by strafing fire. 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, generators, and catapult, but repairs were completed in time for her to launch afternoon strikes as scheduled. Those flights gave chase to the retreating Japanese Center Force.
On 26 October, Sangamon recovered her scattered planes and again launched CAP flights. At 1215, however, enemy planes were reported coming in from the north. Several broke through the air defenses, and Suwanee suffered another kamikaze hit. On 29 October, the escort carriers retired.
On 21 March, Sangamon departed Ulithi with other ships assigned to the Kerama Retto assault force. Covering the force en route, she operated to the south of Okinawa and launched planes for CAP and landing force support as Kerama Retto was secured. On 1 April, as the landings on the Hagushi beaches of Okinawa were taking place, she shifted to TU 52.1.3, thus rejoining her division, CarDiv 22. Through 8 April, however, she continued to launch supporting strikes and patrol groups from an area some south of Okinawa.
On 9 April, she moved, with her unit, into an area east of Sakishima Gunto. From there, her planes raided airfields on Miyako and Ishigaki. Detached on 12 April, she again provided air support for the forces fighting on Okinawa; then covered the occupation of Ie-shima. On 18 April, she returned to Sakishima. Dawn and dusk strikes were launched daily, and heckler flights were sent over the fields at night. On 22 April, eight fighters and four bombers of a dusk strike caught 25 to 30 enemy planes warming up on Nobara Field, central Miyako. Seven "Oscars" attempted to intercept Sangamon's planes, but the attack was pressed home. After delivering their loads, the bombers were sent back to the CVE, while the fighters engaged the "Oscars" and downed five. Night fighters from Sangamon were diverted to the area and arrived as four more enemy planes joined the fight. The latter, also "Oscars", were engaged, and two of the four were shot down before the fight was over.
Through the end of the month, Sangamon continued to launch her planes to neutralize Japanese airfields. On 4 May, she put into Kerama Retto to rearm. Loading, frequently interrupted by the presence of bogies in the area, was not completed until evening. At 18:30, the CVE got underway. Japanese attackers, however, were soon reported only some off. Landbased fighters were vectored out to intercept the enemy planes and shot down nine. One got through and, at about 19:00, began circling toward a position on Sangamon's port quarter. The CVE went into a hard left turn to avoid the enemy and to maneuver into a launching position. She then opened fire and was joined by her escorts. The enemy crashed into the water some off the starboard beam.
Other bogies followed the first. At 19:25, another broke through the interceptor screen, ran into clouds to avoid antiaircraft fire, then came out and, with increased speed, headed for Sangamon. At 19:33, the kamikaze dropped his bomb and crashed into the center of the flight deck. The bomb and parts of the plane penetrated that deck and exploded below - hurling flames and shrapnel in all directions. Initial damage was extensive, fires broke out on the flight deck, the hangar deck, and in the fuel deck, communications from the bridge were lost within 15 minutes; and the ship was soon out of control.
The action of Sangamon swinging through the wind caused the flames and smoke to change direction, spreading the fires. By 20:15, however, steering control had been established, and the ship was brought back to a course which helped the crew fight the myriad fires scattered over the CVE. But water pressure was low; the firemain and risers had ruptured. Carbon dioxide bottles were brought into action. Nearby ships came alongside to assist. By 22:30, all fires were under control. Communication with other units had been regained; at first through the radio of , then by using a VHF channel in the sole remaining aircraft aboard. At 23:20, Sangamon with 11 dead, 25 missing, and 21 seriously wounded, got underway to return to Kerama Retto for temporary repairs.
She was subsequently sold to Hillcone Steamship Company, San Francisco, and was delivered to that company's representative at Norfolk on 11 February 1948. She passed through multiple owners through the 1950s, and ultimately was scrapped in Osaka, Japan starting in August 1960.