See also (David Crockett, the) and how this old weapon made Union History
The Davy Crockett recoilless spigot gun was developed in the late 1950s for use against Soviet armor and troops, had war broken out in Europe. Davy Crockett Sections were assigned to USAREUR [United States Army Europe] armor and mechanized infantry battalions and to straight leg infantry battalions. During alerts to the Inner German border in the Fulda Gap the Davy Crocketts accompanied their battalions. All V Corps (including 3rd Armored Division) combat maneuver battalions had preassigned positions in the Fulda Gap. These were known as GDP (General Defense Plan) positions. The Davy Crockett sections were included in this defense set up. In addition to the Davy Crocketts (e.g., assigned to the 3rd Armored Division), V Corps had nuclear artillery rounds, and these were also targeted on the Fulda Gap.
The M-388 round used a version of the W54 warhead, a very small sub-kiloton fission device. The Mk-54 weighed about 51 lb (23 kg), with a yield equivalent to somewhere between 10 or 20 tons of TNT— very close to the minimum practical size and yield for a fission warhead. The only selectable feature with either versions of the Davy Crockett (M28 & M29) was the height-of-burst dial on the warhead. Post-Davy Crockett versions of the W54 nuclear device apparently had a selectable yield feature ( see below for Hi/Lo Switch and Launching Piston references.) The complete round weighed 76 lb (34.5 kg). It was 31 in. (78.7 cm) long with a diameter of 11 in. (28 cm) at its widest point; a subcaliber piston at the back of the shell was inserted into the launcher's barrel for firing. The "piston" was considered a spigot prior to the discharge of the propellant cartridge in the recoilless gun chamber of the Davy Crockett. The M388 atomic projectile was mounted on the barrel-inserted spigot via bayonet slots. Once the propellant was discharged the spigot became the launching piston for the M388 atomic projectile. The nuclear yield is hinted at in FM 9-11: Operation and Employment of the Davy Crockett Battlefield Missile, XM-28/29 (June 1963).
The M-388 could be launched from either of two launchers known as the Davy Crockett Weapon System(s): the 4-inch (120 mm) M28, with a range of about 1.25 mi (2 km), or the 6.1-in (155 mm) M29, with a range of 2.5 mi (4 km). Both weapons used the same projectile, and were either mounted on a tripod launcher transported by an armored personnel carrier, or they were carried by a Jeep (M-38 & later M-151). The Jeep was equipped with an attached launcher for the M28 or the M29, as required, whereas the Davy Crockett carried by an armored personnel carrier was set up in the field on a tripod away from the carrier. The Davy Crocketts were operated by a three-man crew. In the 3rd Armored Division in Germany in the 1960s many Davy Crockett Sections (all of which were in the Heavy Mortar Platoons, in Headquarters Companies of Infantry or Armor Maneuver Battalions) received what became a mix of M28 & M29 launchers [e.g., one of each per D/C section]. Eventually, the M28s were replaced by M29s, so that both the armored personnel carriers and the Jeeps carried the M29. A Davy Crockett casing preserved in the United States Army Ordnance MuseumBoth recoilless guns proved to have poor accuracy in testing, so the shell's greatest effect would have been its extreme radiation hazard. The M-388 would produce an almost instantly lethal radiation dosage (in excess of 10,000 rem) within 500 feet (150 m), and a probably fatal dose (around 600 rem) within a quarter mile (400 m).
The warhead was tested on July 7, 1962 in the Little Feller II weapons effects test shot, and again in an actual firing of the Davy Crockett from a distance of 1.7 miles (2.72 km) in the Little Feller I test shot on July 17. This was the last atmospheric test detonation at the Nevada Test Site.
Production of the Davy Crockett began in 1956, with a total of 2,100 being made. The weapon was tested between 1962 and 1968 at the Pohakuloa Training Area on Hawaiʻi island, with 714 M101 spotter rounds (not live warheads) that contained depleted uranium. The weapon was deployed with U.S. Army forces from 1961 to 1971. It was deactivated from U.S. Army Europe (in West Germany) in August, 1967.
The 55th and 56th Infantry Platoons, attached to the Division Artillery of the US 82nd Airborne Division, were the last units equipped with the M-29 Davy Crockett weapons system. These two units were parachute deployed and, with a 1/2 ton truck per section, (3 per platoon) were fully air droppable. The units were deactivated in mid-1968.