As 40mm twins gradually became available in 1942 and ’43, they were mounted aft (four barrels total) and later amidships (six barrels), leaving forward-firing secondary defenses to whatever 20mm mounts were available. Ships that had not yet left the states for the war zone were outfitted with additional 20mm forward—one on a platform between the bridge and the “52” mount forward, and one or two on the flying bridge for high bridge ships, and even a third on some low-bridge ships.
When the 10-barrel 40mm configuration began appearing after mid-1943, with the two new 40mm mounts replacing all 20mm forward, the number of 20mm was reduced and standardized at seven—four in the waist and three together in a heart-shaped gun tub on the fantail (top photo).
In 1945, when 40mm quads replaced twins amidships in the final World War II anti-aircraft modification, the single 20mm were also replaced by twin mounts—four in the waist as before but two, rather than three, on the fantail, for a total of 12 barrels.
