Alaska and Guam served with the U.S. Navy during the last year of World War II. Similar to the Iowa-class fast battleships, their speed made them useful as shore bombardment ships and fast carrier escorts. Both protected Franklin when she was on her way to be repaired in Guam after being hit by two Japanese bombs. Afterward, Alaska supported the landings on Okinawa, while Guam went to San Pedro Bay to become the leader of a new task force, Cruiser Task Force 95. Guam, joined by Alaska, four light cruisers, and nine destroyers, led the task force into the East China and Yellow Seas to conduct raids upon shipping; however, they only encountered Chinese junks. By the end of the war, the two had become celebrated within the fleet as excellent carrier escorts. During the war, both ships were part of Cruiser Division 16 commanded by Rear Admiral Francis S. Low, USN.
After the war, both ships served as part of Task Force 71, the designation for the U.S. Seventh Fleet's North China Naval Force. Its mission was to support the allied occupation of the Korean peninsula. This included executing various show-the-flag operations along the western coast of Korea as well as in the Gulf of Chihli. These naval demonstrations preceded Operation Campus, the amphibious landing of U.S. Army ground forces at Jinsen, Korea, on 8 September 1945. Subsequently, both ships returned to the United States in mid-December 1945, and they were decommissioned and "mothballed" in 1947. after having spent 32 months (Alaska) and 29 months (Guam) in service.
In 1958, the Bureau of Ships prepared two feasibility studies to explore whether Alaska and Guam could be suitably converted into guided-missile cruisers. The first study involved removing all of the guns in favor of four different missile systems. At $160 million, the cost of this proposed removal was seen as prohibitive, so a second study was initiated. The study left the forward batteries (the two 12-inch triple turrets and three of the 5-inch dual turrets) unchanged, and added a reduced version of the first plan on the stern of the ship. Even though the proposals would have cost approximately half as much as the first study's plan ($82 million), it was still seen as too expensive. As a result, both ships were stricken from the Naval Vessel Register on 1 June 1960. Alaska was sold for scrap on 30 June 1960, and Guam on 24 May 1961.
The still-incomplete Hawaii was considered for a conversion to be the Navy's first guided-missile cruiser; this thought lasted until 26 February 1952, when a different conversion to a "large command ship" was contemplated. In anticipation of the conversion, her classification was changed to CBC-1. This would have made her a "larger sister" to Northampton, but a year and a half later (9 October 1954) she was re-designated CB-3. Hawaii was stricken from the Naval Vessel Register on 9 June 1958 and was sold for scrap in 1959.