"South Dakota" was built as a fleet flagship, with an extra deck on her conning tower for extra command space, so her secondary battery had sixteen 5-in (127 mm)/38 caliber Mark 12 guns in eight Mark 28 Mod 0 twin DP mounts, four on either side of the superstructure. This was two turrets fewer than her sister ships who had ten twin DP mounts of twenty guns, five on either side of the ship. These turrets weighed 156,295 lb (70,894 kg) and could depress their guns to −15 degrees and elevate them to 85 degrees. The guns fired a variety of different projectiles, including anti-aircraft (AA), illumination, and white phosphorus (WP) shells, at a rate of fire of 15 to 22 rounds per minute. The AA shells were and weighed between 54 and 55 lb (24–25 kg), depending on the variant. The illumination and white phosphorus shells were slightly smaller, at 20 in (50.8 cm) long; the illumination rounds weighed 54.4 lb (24.7 kg) and the WP shells were 53 lb (24 kg).