The Belknap-class cruiser was a class of single-ended guided-missile cruisers built for the United States Navy during the 1960s. They were originally designated as DLG frigates, but in the 1975 fleet realignment, they were reclassified as guided missile cruisers (CG).

The Mark 42 5"/54 caliber gun (127mm) is a naval gun mount used by the United States Navy and other countries. It consisted of the Mark 18 gun and Mark 42 gun mount. United States naval gun terminology indicates the gun fires a projectile 5 inches (127.0 mm) in diameter, and the barrel is 54 calibers long In the 1950s a gun with more range and a faster rate of fire than the 5"/38 caliber gun used in World War II was needed, therefore, the gun was created concurrently with the 3"/70 Mark 26 gun for different usages. The 5"/54 Mk 42 is an automatic, dual-purpose gun mount. It is usually controlled remotely from the Mk 68 Gun Fire Control System, or locally from the mount at the One Man Control (OMC) station.