The "W54" nuclear warhead was used in the weapon known as the "Backpack Nuke"

The "W54" nuclear warhead was used in the weapon known as the "Backpack Nuke"

These small-size devices were first intended for use by United States Army ground soldiers in battle and were in theory small enough to be delivered by a bazooka-style firing mechanism. Early known versions could destroy a two-block area, with an estimated yield comparable to approximately 10 tons of TNT. Larger versions were later developed with a selectable yield of between 10 and 250 tons. Though small compared to most other nuclear weapons, whose yields are usually measured in the thousands of tons of TNT (kilotons), in human terms they are still extremely large – a human might carry on his back 50 kg of chemical explosives, or 0.05 tons. By comparison, the smallest yield version of the W54 (10 tons) is two to four times as powerful as the 1995 Oklahoma City bombing, making the 250-ton version 50 to 100 times as powerful.Several variations of the W54 are known to exist and were used in weapons projects by every branch of the U.S. armed forces except the Coast Guard. The W54 style warhead was known to be used on the M-388 Davy Crockett, a tactical nuclear recoilless rifle projectile that was deployed by the United States during the Cold War. The W54 is small enough to be deployed as a SADM (Special Atomic Demolition Munition), or so-called "Backpack Nuke". It was the closest thing the U.S. is known to have developed to a so-called "suitcase bomb". The W54 was tested for use in a U.S. Navy SEAL project that was demonstrated as feasible in the mid-to-late 1960s, designed to attack a harbor or other strategic location that could be accessed from the sea. The SEAL version would be delivered into water by parachute along with a two-man team, then floated to the target, set in place and armed by hand. The United States Air Force also developed a project using the W54, the Hughes Electronics AIM-26 Falcon. This was a larger, more powerful version of the AIM-4 Falcon air-to-air missile. It is notable for being the only known production U.S. guided air-to-air weapon with a nuclear warhead. It was intended to destroy formations of Soviet bombers at a time when guided missiles were not accurate enough to produce high-probability kills with small conventional warheads.