The original Willys Jeep played many roles in the U.S. armed forces since its debut: ambulance, tow truck, mobile machine-gun mount, scout vehicle, MP patrol car, you name it. But one role it's not widely known for is that of a nuclear launch vehicle.
Let's back up a little before we get to the Jeep part:
The miniaturization of nuclear devices became a priority even before the first device was tested in 1945: The warheads were of little use if they could not be delivered to the target area by bomber aircraft. As the early fission devices used against Japan in August 1945 were roughly the size of actual Jeeps and weighed around 10,000 pounds each, miniaturization and the need to fit more than one device per plane was a priority for Air Force squadrons charged with delivering the weapons.
Advances in nuclear weapon technology and smaller warhead designs in the 1950s led to new missions for nuclear weapons beyond large, strategic targets. The maximum practical level of miniaturization resulted in the W54 warhead, developed for the M-388 round for a recoilless rifle. The warhead could be fired by what amounted to a tripod-based spigot gun that could also be fitted to a small vehicle such as the ubiquitous Jeep, and the weapon system itself was christened the M28 Davy Crockett.