During the initial period of the Cold War, there was a boom in military innovation as the United States and the Soviet Union engaged in a nuclear arms race to produce potent and versatile nuclear weapons. Both powers sought to integrate atomic firepower with traditional forces, and for the U.S. Army, this consisted of nearly undertaking a grand project: the design of a nuclear-tipped artillery piece. This project spawned the M65, better known as “Atomic Annie”—a weapon that soon became a symbol of Cold War brinksmanship but ultimately proved to be a technological dead end.
The Atomic Annie story starts in the early post-World War II years, when American engineers examined the German Krupp K5 railway guns, which Allied soldiers had dubbed “Anzio Annie.”. The ultimate question was whether the explosive force of atomic bombs—the weapons that brought about the end of the Pacific War—could be translated into a form employable by ground troops on the battlefield.
The Pentagon tasked Picatinny Arsenal in New Jersey with this mission, where engineer Robert Schwartz got to work designing a huge artillery weapon. His design took much of the German guns’ design, but for road mobility, not railways.
What came out was the M65: a wonder of mid-20th-century engineering. It was a whopping 85 feet long and tipped the scales at over 170,000 pounds. It took two specially built tractors to move it, and it took a team of up to seven soldiers to crew the cannon. Its 280mm barrel could fire a nuclear shell up to 20 miles, and despite the huge size, the gun could be prepared for firing or movement in less than 30 minutes—an achievement unprecedented at the time.
On a ball-and-socket joint, it had limited horizontal mobility, and wherever it was seen, the sheer size of the weapon attracted stares. A prototype even appeared in President Dwight D. Eisenhower’s first inaugural parade in January 1953, showing just how fast the project had developed.
The real test of Atomic Annie occurred on May 25, 1953, at the Nevada Test Site during Operation Upshot-Knothole, a set of nuclear tests aimed at assessing new weapons and tactics. The artillery shell, which was referred to as “Shot Grable,” was the only nuclear detonation ever discharged from a cannon. The Army personnel from Fort Sill, Oklahoma, loaded an 11-inch, 800-pound W9 nuclear shell into Annie’s barrel. At 8:30 a.m., the gun boomed into action, propelling the shell on a flight of 19 seconds before it burst in an airburst about six miles out, having a yield of 15 kilotons—similar to the one that had been dropped over Hiroshima.
Thousands of soldiers, scientists, and officials were present for the test, many taking part in training drills that tested how troops and equipment would stand up to a nuclear attack. The blast generated a characteristic mushroom cloud, and the shock wave generated a rare “precursor” shock front that left characteristic damage on adjacent vehicles and buildings. The test demonstrated that nuclear artillery was feasible, but it was also the single instance that the U.S. ever fired a live atomic shell from a cannon.
Following the successful trial, the Army bought around 20 M65 cannons, each priced at approximately $800,000—a considerable amount at that time. The cannons were based in Europe, Korea, and Okinawa and were frequently shifted to avoid enemy targeting. Nevertheless, the M65’s operational life was short.
Advances in warhead miniaturization came soon enough for atomic shells to be accommodated in standard 155mm and 203mm artillery, and the advent of tactical missiles and rockets shortly rendered the cumbersome M65 obsolete. The gun was formally retired in 1963, barely a decade after its spectacular introduction.
Atomic Annie’s history contains some peculiar incidents. During the confusion of Cold War deployments, the original test gun and its backup, dubbed “Sad Sack,” were accidentally swapped. This mix-up went unnoticed for a decade until preparations for the Grable test’s tenth anniversary uncovered the mistake.
The quest for the real Annie, once dubbed “AWOL Annie,” concluded with her recovery in Germany and return to Fort Sill, where she now rests on exhibit at the U.S. Army Field Artillery. Several other M65s remain in museums throughout the nation, quiet reminders of an era when the globe experimented briefly with nuclear artillery on the battlefield.
Even though Atomic Annie never saw action, her legacy is a strong representation of the frenzied innovation and strategic uncertainty that characterized the earliest Cold War era. The brief functional role of the gun as a weapon underscores how rapidly military technology developed under the nuclear era—what was once the tip of the technological spear would become outdated all too soon. For historians and tankers alike, Annie’s story provides an interesting glimpse into the optimism, difficulties, and constraints of nuclear artillery.