Suitcase nukes may be just be a myth

http://www.damninteresting.com/?p=783#more-783

The Atomic Battle Group was charged with the protection of Europe between 1961 and 1971, and during those ten years 2,100 of the Davy Crockett Weapons Systems were deployed. In the event of a Soviet invasion, these elite squads were trained to deploy themselves in the path of the advancing formations. Once in position, a flurry of mathematics would provide the trajectory and flight time to the targets, and these data would be used to configure the launchers for maximum carnage. A test shot with the integrated 37mm spotting gun would verify the operators' angle and timing calculations. The three men would then unpack a shell from its carrying case, set the timer knob to detonate the warhead roughly twenty feet above the target, and dial in their preferred yield of ten or twenty tons.

Upon receiving the order to fire, Davy Crockett would leap from its perch with a bang and a cloud of smoke, racing through sky in a long arc to intercept the advancing enemy. The rudimentary atomic bomb did not include an abort feature, so Davy Crockett was committed to destruction once it was en route. Even with the help of the spotter gun and rifled barrel, both of the Davy Crockett launcher designs were somewhat sloppy in their accuracy, so the detonation was likely to be several hundred feet from the target. Moreover, the shells' relatively small yield didn't produce a great deal of blast damage even at the highest setting. But the weapon's tendency to spew radiation over the battlefield made up for its shortcomings as an explosive.

Less than a minute after launch, the detonation timer would tick off its final second over the target area. Few specifics are available about the weapon's internals, but it is likely that it contained a thirty pound hollowed-out wad of plutonium wrapped in beryllium and shape charges. Upon detonation, the shape charges would use a precision shock wave to crush the cavity in the center of the plutonium and press the nuclear material into a small area. Radioactive nuclei tend to eject neutrons, and once the material is crowded into a tiny space these flying neutrons start to hit and split the nuclei of neighboring plutonium atoms. As each atom splits, an abrupt spray of energy is released as well as more neutrons which can go on to split even more nuclei.