In 1941 the standard light anti-aircraft gun for the US Navy was the .50 caliber machine gun and the standard medium gun was the quadruple 1.1-inch "Chicago Piano". The machine gun was far too light and the 1.1-inch gun was a flop, too heavy and prone to jamming. The USN found excellent substitutes in the form of the Swiss 20mm Oerlikon and Swedish 40mm Bofors guns. By 1944 the Oerlikon was past its prime and efforts were made to increase the Bofors count and reduce Oerlikons. By 1945 even the Bofors gun was loosing its efficiency in face of larger and faster aircraft guns. After the war the USN replaced the quadruple Bofors mount with twin 3-inch mounts but that merely provided a stop gap measure. Even these guns were marginally effective against the speed of jet aircraft. To counter the jet threat guided missiles were necessary. Rather than go through the long development time necessary for a completely new design, it was thought to be much quicker and cheaper to convert some of the vast number of war built cruisers to carry guided missiles. The first consideration was hull size.
The new Terrier missile was bulky but not especially heavy. The Baltimore Class heavy cruisers had the necessary internal volume to convert to missile cruisers, so USS Boston CA-69 and USS Canberra CA-70 were selected for conversion to missile cruisers, becoming CAG-1 and CAG-2. Their designation was CAG, reflecting retention of their gun capability with the addition of guided missile capability. They became the first ships of the new USN missile fleet. Conversion started in 1952 and was finished in 1955 and 1956. The aft 8-inch turret was replaced by two twin Terrier mounts and associated guidance radar. Each mount had its own magazine, which stored 144 missiles. The Terrier had a limited range of around twelve miles and soon relegated to a secondary role with the introduction of the much longer ranged Talos missile. The twin stacks were combined into a much larger single stack. By 1970 the Terrier was obsolete and both ships were scrapped. Thanks to Argos you can get a 1:1250 scale USS Boston CAG-1, which is wonderfully detailed.
Argos AS-95 USS Boston CAG-1 is available from 1250Ships.com for all of you aspiring missile maniacs.