More powerful than the 16"/45 (40.6 cm) Mark 6 guns used on the North Carolina (BB-55) and South Dakota (BB-57) classes, this was possibly the best battleship gun ever put into service. Originally intended to fire the relatively light 2,240 pound (1,016.0 kg) AP Mark 5 projectile, the shell handling system for these guns was redesigned to use the "super-heavy" 2,700 pound (1,224.7 kg) AP Mark 8 before any of the USS Iowa class (BB-61) battleships were laid down. This heavier projectile made these guns nearly the equal in terms of penetration power to the 46 cm (18.1") guns of the Japanese Yamato class battleships, yet they weighed less than three-quarters as much.

As modernized in the 1980s, each turret carried a DR-810 radar that measured the muzzle velocity of each gun, which made it easier to predict the velocity of succeeding shots. Together with the Mark 160 FCS and better propellant consistency, these improvements made these weapons into the most accurate battleship-caliber guns ever made. For example, during test shoots off Crete in 1987, fifteen shells were fired from 34,000 yards (31,900 m), five from the right gun of each turret. The pattern size was 220 yards (200 m), 0.64% of the total range. 14 out of the 15 landed within 250 yards (230 m) of the center of the pattern and 8 were within 150 yards (140 m). Shell-to-shell dispersion was 123 yards (112 m), 0.36% of total range.

The Armor Piercing (AP) shell fired by these guns is capable of penetrating nearly 30 feet (9 m) of concrete, depending upon the range and obliquity of impact. The High Capacity (HC) shell can create a crater 50 feet wide and 20 feet deep (15 x 6 m). During her deployment off Vietnam, USS New Jersey (BB-62) occasionally fired a single HC round into the jungle and so created a helicopter landing zone 200 yards (180 m) in diameter and defoliated trees for 300 yards (270 m) beyond that.

A persistent anecdote is that the Iowa class suffered from alignment problems until after the Battle of Leyte Gulf. William Jurens, a noted expert on US naval weaponry, together with Iowa crewmembers and the staff at NSWC Dahlgren, performed a search of the official records for detailed data on this specific problem, but could find nothing in the files suggesting that the alignments were in any way out of the ordinary. Mr. Jurens' suspicion is that there may have been an oblique reference to an alignment problem in some document that was taken out of context; perhaps they were waiting for parts.

The Iowa class battleships are the sole survivors of the battleship era that can still be placed into service, although they now exist mainly as memorials.

The weapon is constructed of liner, A tube, jacket, three hoops, two locking rings, tube and liner locking ring, yoke ring and screw box liner. Some components were autofretted. As typical of USN weapons built in the 1940s, the bore was chromium plated for longer barrel life. Uses a hydraulically operated Welin breech block which opens downwards. The screw box liner and breech plug are segmented with stepped screw threads arranged in fifteen sectors of 24 degrees each.