The fifth USS Boxer (CV 21) was launched December 14, 1944 by Newport News Shipbuilding and Dry Dock Co. Newport News, Va.; sponsored by Miss Ruth D. Overton daughter of the Senator from Louisiana and commissioned April 16, 1945, Captain D. F. Smith in command.

Completed too late to take part in World War II, Boxer joined the Pacific Fleet at San Diego in August 1945. From September 1945 to August 23, 1946 she operated out of Guam as flagship of TF 77 in the western Pacific. During this tour she visited Japan, Okinawa, the Philippines and China. She returned to San Francisco September 10, 1946 and operated off the west coast engaged in normal peacetime duty until departing for the Far East January 11, 1950. After service with the 7th Fleet in the Far East during the first half of 1950, she returned to San Diego, arriving June 25th.

With the outbreak of the Korean conflict she was pressed into service to carry planes to the fighting. On July 23, 1950 she completed a record crossing of the Pacific from Alameda, Calif., to Yokosuka, Japan, in 8½ days, carrying 145 P-51 Mustang and six L-5 aircraft for the Air Force, 19 Navy planes, 1,012 troops and 2,000 tons of supplies. On her return trip (July 27- August 4), she cut the record to 7 days, 10 hours, and 36 minutes. After fast repairs she departed for the Far East August 24, this time to join TF 77 in giving air support to the troops. Her planes supported the landing at Inchon (September 15, 1950) and other ground action until November, when she departed for the west coast and overhaul.

USS Boxer (CV 21) departed San Diego for her second Korean tour March 2, 1951. Again she operated with TF 77 supporting the ground troops. On March 29, Carrier Air Wing 101, composed of Naval Reserve squadrons called to active duty from Dallas, Tex.; Glenview, Ill.; Memphis, Tenn.; and, Olathe, Kans., flew its first combat mission from Boxer, the first carrier strikes by Naval Reserve units against North Korean forces. She returned to San Francisco October 24, 1951.

Sailing February 8, 1952 for her third tour in Korea, USS Boxer again served with TF 77. On June 23, 35 AD Skyraiders and 35 F-9F2 Panther jets from Boxer, USS Princeton (CV 37) and USS Philippine Sea (CV 47), joined Air Force Thunderjets in an attack on the heavily defended hydroelectric power plant at Suiho, North Korea, the fourth largest such facility in the world. The plant was completely knocked out. The raid was part of a two-day aerial offensive against North Korea's 13 major power plants.

On August 5, 1952, Boxer had nine men killed and two seriously injured in a fire which swept the hangar deck. After emergency repairs at Yokosuka, Japan (August 11-23rd), the carrier returned to duty off Korea. It arrived at San Francisco September 25 and underwent repairs until March 1953.

The carrier departed for the Far East March 30, 1953 and went into action a month later. She took part in the final actions of the Korean conflict and remained in Asiatic waters until November.

USS Boxer was reclassified CVA 21 on October 1, 1952 and CVS 21 on February 1, 1956.

On October 2, 1958, the Commander in Chief, U.S. Atlantic Fleet, announced the formation of a new amphibious squadron, composed of Boxer and for LSDs equipped with helicopter platforms, which would provide a highly mobile unit capable of employing Marine Corps helicopters squadrons and combat troops in the fast-landing concept of vertical envelopment. The first permanent Marine Aviation Detachment afloat was activated on board Boxer on November 10th to provide supply, maintenance, and flight deck control functions necessary to support the Marine helicopter squadrons and troops. The ship was reclassified as LPH 4 on January 30, 1959.

USS Boxer and two LSDs arrived off the coast of Hispanola on August 29, 1964 to provide medical aid and helicopter evacuation services to people in areas of Haiti and the Dominican Republic badly damaged by Hurricane Cleo. Boxer returned to the Dominican Republic on April 27, 1965, sending her Marines ashore while the embarked HMM-264 began an airlift in which over 1,000 U.S. nationals were evacuated to the naval task force off shore as a revolt in the country threatened their safety.

Boxer also participated in the U.S. space program. On February 26, 1966, the first unmanned spacecraft of the Apollo series, fired into suborbital flight by a Saturn 1B rocket from Cape Kennedy, Fla., was recovered in the southeast Atlantic Ocean, 200 miles east of Ascension Island by a helicopter from the ship.

USS Boxer (LPH 4) was decommissioned December 1, 1969, and striken from the Navy List. She was sold for scrapping on March 13, 1971.