# W79

The **W79** was an American nuclear artillery shell, capable of being fired from any standard 8 inch (203 mm) howitzer e.g. the M115 & M110 howitzer.[1]

The **W79** was produced in two models, the "W79 Mod 0" and "W79 Mod 1". Both were a plutonium-based linear-implosion, nuclear weapon.

The "Mod 0" was a variable yield device with three yields, ranging from 100 tons up to 1.1 kiloton and an enhanced-radiation (popularly known as neutron bomb) mode which could be turned on or off.[2]

The "Mod 1" was fission only, without the enhanced-radiation option, and had a fixed 0.8 kiloton yield (800 tons of TNT). This probably corresponds with the maximum pure-fission yield of the "Mod 0".

Both models were 8 inches (203 mm) in diameter, 44 inches (112 cm) long and weighed 200 pounds (90 kg).

The **W79** was produced starting at least as early as 1976 and continuing into 1986. All units were retired from active service by the end of 1992.

## Linear implosion

Linear-implosion uses a mass of nuclear material which is more than one critical mass at normal pressure and in a spherical configuration. The mass, known as pit, is configured in a lower density non-spherical configuration prior to firing the weapon and then, small to moderate amounts of explosive collapse and slightly reshape the nuclear-material into a supercritical-mass which then undergoes chain-reaction and explodes. Three methods are known to compress and reshape the nuclear-material: 1) collapsing hollow spaces inside the nuclear material; 2) using plutonium-gallium alloy, which is stabilized in the low-density delta-phase at a density of 16.4 (and which collapses to denser alpha-phase under moderate explosive-compression); and 3) shaping an explosive and nuclear material so that the explosive pressure changes a stretched-out, elliptical or rugby-football shape to collapse towards a spherical or more spherical end-shape.

A bare critical mass of plutonium at normal density and without additional neutron reflector material is roughly 10 kilograms. To achieve a large explosive-yield, a linear-implosion weapon needs somewhat more material, on the order of 13 kilograms. 13 kilograms of alpha-phase (highest density) plutonium at a density of 19.8 g/cmÂ³ is 657 cubic centimeters, a sphere of radius 5.4 cm (diameter 10.8 cm / 4.25 inches).

Linear-implosion weapons could use tampers or reflectors, but the overall diameter of the fissile-material plus tamper/reflector increases compared to the volume required for an untamped, unreflected pit. To fit weapons into small artillery-shells (155 mm and 152 mm are known; 105 mm has been alleged to be possible by nuclear-weapon designer Ted Taylor), bare pits may be required.

Linear-implosion weapons have much lower efficiency due to low pressure, and require two to three times more nuclear-material than conventional implosion weapons. They are also considerably heavier, and much smaller than conventional implosion weapons. The W54 nuclear warhead used for special purposes and the Davy Crockett nuclear-artillery unit was about 11 inches diameter and weighs 51 pounds. The 155 mm W48 is 6 inches in diameter and weighs over twice as much, and probably requires twice as much plutonium. Independent researchers have determined that one model of US Army conventional implosion fission-weapon cost $1.25 million per-unit produced, of which $0.25 million was the total cost for all non-nuclear components and $1 million the cost of the plutonium. Linear-implosion weapons, requiring two to three times more plutonium, are considerably more expensive.