USS Kentucky (BB-66) was an uncompleted battleship intended to be the last ship of the Iowa class. Hull BB-66 was originally to be the second ship of the Montana-class battleships. However, the urgent need for more warships at the outbreak of World War II and the U.S. Navy's experiences in the Pacific theater led it to conclude that rather than battleships larger and more heavily armed than the Iowa class, it quickly needed more fast battleships of that class to escort the new Essex-class aircraft carriers being built. As a result, hulls BB-65 and BB-66 were reordered and laid down as Iowa-class battleships in 1942.

The Iowa class was a class of six fast battleships ordered by the United States Navy in 1939 and 1940. They were initially intended to intercept fast capital ships such as the Japanese Kongō class and also serve as the "fast wing" in a traditional battle line alongside slower battleships. The Iowa class was designed to meet the Second London Naval Treaty's "escalator clause" limit of 45,000-long-ton (45,700 t) standard displacement. Beginning in August 1942, four vessels, Iowa, New Jersey, Missouri, and Wisconsin, were completed; two more, Illinois and Kentucky, were laid down but canceled in 1945 and 1958, respectively, before completion, and both hulls were scrapped in 1958–1959.