Muzzle velocity
"Iowa" was armed with a main battery of four /35 caliber guns mounted in two twin-gun turrets that were mounted on the centerline, one forward and the other aft of the superstructure. The built-up guns were the Mark II type, which were placed in elliptical Mark III turrets. The training gear was hydraulically operated, but elevation was hand-operated only. The gun mounts allowed elevation to 14 degrees and depression to −5 degrees; to reload the guns, they had to be returned to 3 degrees elevation. The ammunition hoists that retrieved shells and propellant charges from the magazines were also hydraulically operated. The guns fired an shell with a charge of brown powder. Muzzle velocity was , and at the muzzle, the shells could penetrate up to of mild steel; at a range of , their penetration capability fell to . The average rate of fire was one shot every five minutes, though fresh, well-trained crews could achieve rates as fast as one shot every three minutes.