US Navy Iowa-class battleships could have fired nuclear bombs

Key points from this article: Towards the end of World War II, advances in military technology made traditional battleship guns less decisive. In response, the U.S. Navy in the 1950s investigated arming its Iowa-class battleships with nuclear artillery shells, known as “Katie” (Mk 23) shells.

-These 16-inch nuclear shells had a force comparable to the bombs dropped on Hiroshima and could be fired from the battleships’ existing guns without modification.

– Approximately 50 such shells were produced, and storage modifications were carried out on three Iowa-class ships. Although it is unclear whether these battleships ever carried nuclear shells during active service, all Mk 23 shells were withdrawn in 1962 without ever seeing combat use.

From Big Guns to Nuclear Shells: The Evolution of the US Navy’s Battleships

In the battleship era, it was the big guns that were the real hallmarks of the ships. By the end of World War II, however, new technologies were coming onto the market – and it was clear that those big guns simply wouldn’t cut it in future conflicts.

The US Navy considered transforming its largest combat ships and giving them some more firepower: nuclear firepower.

As previously reported by The National Interest, the U.S. Navy first proposed the Iowa-class ships by removing all of the 16-inch guns and replacing them with anti-aircraft and anti-submarine missiles. As “guided missile battleships,” each would also carry four Regulus II cruise missiles, each capable of destroying a city a thousand miles away with a warhead more than 100 times more powerful than the bomb used on Hiroshima.

The result would certainly have been the most powerful battleship ever built, but as previously reported, it was also riddled with a significant number of inefficiencies—most notably the fact that an Air Force bomber could attack just as many targets, at greater range, and require far fewer personnel. Furthermore, the conversion, with a price tag of $1.5 billion in 2020, would have been expensive.

The Iowa Class and Its Big Guns

The US Navy also considered another option: one that would retain the big guns but add a very special round.

With a primary armament consisting of nine 16-inch (406mm)/50-caliber guns in three 3-gun turrets, including two forward and one aft, the four U.S. Navy ships were Iowa-class battleships were the most powerful warships built by the United States during World War II. Each of those guns was 66 feet (20 meters) long, which was 50 times their 16-inch bore (50-caliber) from breech to muzzle.

Each of the guns weighed approximately 239,000 pounds (108,000 kg), while the projectiles weighed from 1,900 to 2,700 pounds (850 to 1,200 kg) and had a maximum velocity of 2,690 feet per second with a range of 24 miles (39 km). At maximum range, the projectiles would remain aloft for nearly a minute and a half.

While that was impressive, in the early stages of the Cold War in 1953, the U.S. Navy began a top-secret program to develop Mk 23 “Katie” naval nuclear shells, which reportedly had an estimated yield of 15 to 20 kilotons. Designed to be launched from the best naval artillery platforms of the time, which happened to be the four Iowa-class battleships, The grenades could have given the navy considerable striking power.

At the time the shells were being developed, the U.S. military had aircraft and missiles capable of delivering nuclear weapons, but it was found that the Mk 23/Mark 7 16-inch gun combination could provide an extremely accurate platform that was usable in all weather conditions – compared to early jet aircraft and even missiles that were grounded in bad weather.

Production of the grenades appears to have begun in 1956, and approximately 50 of the special nuclear grenades are believed to have been produced. Each was approximately 410 mm in diameter, while each was 160 cm long and weighed 680 to 860 kg. It has been suggested that the projectiles may have been installed in an otherwise unmodified HC Mk 13 grenade casing, but other sources note that the Katie projectile was slightly smaller than the Mk 13.

According to GlobalSecurity.com, USS Iowa (BB-61), USS New Jersey (BB-62) and USS Wisconsin (BB-64), each had a modification to its Turret II magazine to integrate and secure storage areas for the projectiles. A total of 10 of the nuclear grenades, along with nine Mk 24 practice grenades, could be stored in the secure storage area. USS Missouri (BB-63) was placed in the reserve fleet in 1955 and was therefore never modified to accommodate the nuclear shells.

As Brent Eastwood reported, “Each ship would carry ten Katie projectiles and nine practice rounds. This would give the Navy the largest and most powerful nuclear artillery in the world—a total of 135–180 kilotons of yield.”

Although the weapons themselves were not modified, the introduction of the Katie grenades ensured that the Iowa-class battleship’s 16-inch guns were the largest nuclear artillery in the world. They were also the only U.S. Navy warships potential armed with nuclear grenades – and it is still unknown whether any of the three combat vehicles ever actually carried the grenades in active service. The U.S. Navy’s policy is neither to confirm nor deny the presence of nuclear weapons aboard its ships.

However, it is known that all nuclear projectiles had been withdrawn from service by October 1962, and that none were ever fired from the 16-inch guns. Wisconsin had fired one of the practice shells during a test in 1957, while one of the projectiles was expended as part of Project Plowshare, which was the peaceful use of nuclear explosives for construction purposes. An inert Mk 23 shell body is currently on display at the National Atomic Museum in Albuquerque, New Mexico.

Author Experience and Expertise: Peter Suciu

Peter Suciu is a writer from Michigan. He has contributed to more than four dozen magazines, newspapers, and websites with more than 3,200 published pieces in a two-decade career in journalism. He writes frequently about military equipment, firearms history, cybersecurity, politics, and international affairs. Peter is also a Contributing Writer for Forbes and Clearance jobsYou can follow him on Twitter: @PeterSuciu. You can email the author: (email address).

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