W23

The W19 under the designation W23 was adapted for 16-inch / 410 mm battleship guns. Production of the W23 began in 1956, and they were in service until 1962, only 50 were produced. The diameter of W23 was 410 mm, length - 160 cm, weight 680 - 860 kg. Its yield was also 15-20 kt.

A total of fifty Mark 23 "Katie" nuclear projectiles were produced during the 1950s with development starting in 1952 and the first service projectile being delivered in October 1956. It is possible that the W23 nuclear warhead used for this projectile may have been installed inside of an otherwise unaltered HC Mark 13 shell body, although one of the source says that the projectile was slightly smaller than the Mark 13.

USS Iowa, USS New Jersey and USS Wisconsin had an alteration made to Turret II magazine to incorporate a secure storage area for these projectiles. USS Missouri was not so altered as she had been placed in reserve in 1955. This secure storage area could contain ten nuclear shells plus nine Mark 24 practice shells.

The shell's introduction made the Iowa-class battleship's 16 in guns the world's largest nuclear artillery, and made these four battleships the only U.S. Navy ships ever to have nuclear shells for naval guns. Although developed for exclusive use by the battleship's guns it is not known if any of the Iowa-class battleships actually carried these shells while in active service due to the United States Navy's policy of refusing to confirm or deny the presence of nuclear weaponry aboard its ships.

These nuclear projectiles were all withdrawn from service by October 1962 with none ever having been fired from a gun. One projectile was expended as part of Operation Plowshare (the peaceful use of nuclear explosive devices) and the rest were deactivated. USS Wisconsin did fire one of the practice shells during a test in 1957.

At least one Mark 23 shell body still exists at the National Atomic Museum in Albuquerque, New Mexico, as can be seen in the photograph below.