its the tyoe of gun

The Iowa-class battleships, four of which were built:

USS Iowa (BB-61)

USS New Jersey (BB-62)

USS Missouri (BB-63)

USS Wisconsin (BB-64)

USS Iowa (BB 61) - San Francisco, California (Planned)

USS New Jersey (BB 62)- Camden, New Jersey

USS Missouri (BB 63 ) - Pearl Harbor, Hawaii

USS Wisconsin (BB 64) - Norfolk, Virginia

USS Massachusetts (BB 59) - Fall River, Massachusetts

USS North Carolina (BB 55) - Wilmington, North Carolina

USS Alabama (BB 60) - Mobile, Alabama

USS Texas (BB 35) - La Porte, Texas

Every vessel of the US Navy (as in almost all other navies) is given a ship number within its class, as well as a name. The last US battleships were the USS Wisconsin (BB 64) and the USS Iowa (BB 61), which were removed from the Naval Register on March 17, 2006, having been decommissioned in 1992 and 1990 respectively.

Federal regulations currently state that the Navy must retain 2 Iowa-class battleships for retention and service should the need to recall them ever occur. The USS New Jersey (BB-62) and the USS Missouri (BB-63) are both currently serving as museum ships. The USS Iowa (BB-61) and the USS Wisconsin (BB-64) are currently the only 2 that could be recalled. However, given the damage sustained by the Iowa as a result of her powder charge explosion in the forward gun turret, it's likely the Wisconsin would be the likely first choice for any recall, since she's in much better shape.