This class was kind of a white elephant in the Navy. Its design history began in the late 1930's, when the Navy ran wild with rumors of a Japanese merchant raider (which may or may not have been called Chichibu). This ship, which was presumed to be an improvement of the German "pocket-battleship" idea of the Deutschland class, would have been kind of a threat to the pre-war navy, not relying on carriers for anything but reconnaisance.

    But the Japanese, if they ever really thought about building this ship (which, given their Mahanian tradition of "defeating the fleet", is doubtful), were soon to cancel the project. The US Navy, however, designed a warship that would be able to sink the raider easily, through high speed and heavy guns.  For this class, the Navy ordered a new gun, 305mm L/50, and build these guns into a new turret.

    The design called for a ship of cruiser protection, and roughly 30.000 tons standard displacement. To reach the desired top speed of 33 knots, the class received the same propulsion plant that the Essex class had.  
  While these ships were a proper design, for their task, by the time of their commision, 1944, they were useless in their scheduled role. As carriers would have easily dealt with any merchant raider, having a longer range, better scouting capability, and larger punch, while having the same speed, and there were no more merchant raiders in any of the Axis navies, the two ships that were completed were used as fast carrier escorts.  
  Alaska and Guam were both escorting US fast carriers across the Pacific, starting in early 1945. They were, due to their obsolee rôle, decommisioned in 1947 and scrapped up later.