W79 Artillery-Fired Atomic Projectile

The W79 Artillery-Fired Atomic Projectile (AFAP), also known as XM753 (Atomic RA), was an American nuclear artillery shell, capable of being fired from any NATO 8 in howitzer e.g. the M115 and M110 howitzer. The weapon was produced in two models; the enhanced radiation (ERW) W79 Mod 0 and fission-only W79 Mod 1. Both were plutonium-based linear-implosion nuclear weapons.
 * The Mod 0 was a variable yield device with three yields, ranging from 100 tonTNT up to 1.1 ktonTNT and an enhanced-radiation mode which could be turned on or off
 * The Mod 1 was fission-only with a fixed 0.8 ktonTNT yield, corresponding with the maximum fission only yield of the Mod 0

Both models were 8 in in diameter, 44 in long and weighed 200 lb. The W79 was developed by Lawrence Livermore National Laboratory, starting in 1975. Production of the different mods took place from July 1981 through August 1986. A total of 550 warheads (325 Mod 0s, 225 Mod 1s) were produced. All units were retired from active service by the end of 1992 with the last shell dismantled at the Pantex Plant in Texas in August 2002.

History
The weapon received Phase 3 authorisation in January 1975 and cleared a critical budget review before the Joint Committee on Atomic Energy in April 1975.

First production unit was in July 1981. Quantity production on the standard (non-ERW) W79-1 version of the weapon began in September 1981 and continued until the summer of 1984. Production of the ERW W79-0 version began in 1984 and continued until August 1986.

During development, some part of the weapon was deemed too impractical to manufacture and a significant design revision was undertaken. This design changed the physics behaviour of the weapon and a new nuclear test was required to certify the new design.

In early 1988, a new 3-dimensional computer simulation suggested that the weapon was not one-point safe under certain conditions. Nuclear testing carried out in December 1988 and February 1989 confirmed these findings.

Design
The weapon had a range of 24 km or 30 km with rocket assist.

The weapon utilized the M735 proximity fuze. It contained a dual-channel fuze system, target sensor, electronic programmer and power supply. Its design goals were to minimize overall weight, minimize structural volume, eliminate the use of potting materials for structural support, and to eliminate cable and wire harnesses. The goal of not using potting materials was ultimately not met.

The fuze was developed with an extensive test firing program and in service use would have experienced a 10400 g0 setback acceleration and 11400 rpm spin. Some test units experienced setbacks of 15300 g0.

During early development, the intermediate cost Nonviolent Explosive Destruct System (NEDS) was selected to secure the weapon against unauthorised use. This system was tested at Tonopah Test Range.