Nuclear weapons are very big and very powerful, thus they require very big and very powerful delivery systems. In the early 1950s, the sheer size of nuclear bombs required massive aircraft such as the B-29 Superfortress as the means of delivery. The United States Military considered nuclear bombs were the future of warfare but began to look at alternative methods to deploy them, which led to the Atomic Cannon.
The M65 Atomic Cannon more commonly known as Atomic Annie was a huge artillery weapon capable of launching a nuclear device. The explosion and fallout from a nuclear blast were incredibly dangerous so the cannon was actually able to launch bombs over a distance of 20 miles.
In total, the United States Military manufactured 20 of the M65 Atomic Cannons and dispatched them to Korea and Europe as deterrents for hostile communist nations. In the end, the atomic cannon did not get a whole lot of use due to its limited firing range and incompatibility with advancing nuclear weaponry. Launching nuclear weapons artillery was simply irrelevant compared to bombings or guided rocket-based delivery systems.
Although the M65 never saw any real combat the test footage showcasing the raw power of the weapon is mesmerizing.