The ships had a variety of anti-aircraft weapons, and the weapons mounted changed over time. Initially, the ships were designed to mount twelve and twelve machine guns. By March 1942, when "South Dakota" was completed, the anti-aircraft battery was modified to eight and twenty-eight machine guns and sixteen 20mm Oerlikon autocannon. In September of that year, the guns were removed and the number of guns reduced to 20. In their place, the 20mm guns were increased to 16 weapons, and 16 Bofors 40mm guns were added, in four quadruple mounts.