The US has developed several nuclear artillery shells in the 155 mm caliber. The only one to be deployed was the W-48 nuclear warhead developed by UCRL, packaged in the M-45 AFAP (artillery fired atomic projectile) shell. The W-48 nuclear warhead measured 86 cm (34") long and weighed 53.5-58 kg (118-128 lbs). Its yield was on the order of 70 to 100 tons (it was tested in the Hardtack II Tamalpais shot with a yield of 72 tons, predicted yield was 100-300 tons).
The smallest diameter US test device publicly known was the Livermore Swift device fired in the Redwing Yuma shot on 28 May 1956. It had a 5" (12.7 cm) diameter, a length of 62.2 cm (24.5 inches) and weighed 43.5 kg (96 lb). The test had a yield of 190 tons, but was intended to be fusion boosted (and thus would probably have had a yield in the kiloton range) but its yield was insufficient to ignite the fusion reaction and it failed to boost in this test. This test may have been a predecessor to the W-48 design.
The W-48 was 846 mm long and weighing 58 kg, it could be fitted in a 155 mm M-45 AFAP (artillery fired atomic projectile) and used in the standard 155 mm howitzer. The fission warhead was a linear implosion type, consisting of a long cylinder of subcritical mass which is compressed and shaped by explosive into a supercritical mass. The W-48 yielded just 72 tons TNT equivalent. The W-48 entered production in 1963, and 135 of the Mod 0 variant were built. The Mod 0 variant was retired in 1968. It was retired. It was replaced by the Mod 1 which was manufactured from 1965 through 1969, with 925 of this type being built.
In 1939, J. Robert Oppenheimer had first proposed a uranium hydride nuclear fission bomb to utilize the deuterium hydrogen isotope in a U235 metal-deuterium compound. The design used uranium-hydride 235, which featured the absorption of low-velocity neutrons by uranium, providing a lower critical mass. But the hydrogen slows the process, possibly to impermissibly long periods of time. Weapon efficiency is adversely affected by the slowing of the neutrons, since it gives the bomb core more time to blow apart. The nuclear fission chain reaction would be the result of slow (thermal energy) neutron fission, with a predicted energy yield of 1,000 tons TNT equivalent.
After the war Edward Teller remained interested in the development of the uranium hydride bomb. Ruth and Ray were both uranium hydride experimental devices designed by Edward Teller and Ernest Lawrence at UCRL, later the Lawrence Livermore National Laboratory (LLNL). Ruth was the first device fielded by UCRL and was detonated 31 March 1953; Ray was detonated 11 April 1953. Both yielded an energy of explosion equivalent to 200 tons of TNT.
Lawrence Livermore National Laboratory was less than a year old when the first nuclear-explosive device designed entirely by Livermore scientists was fired at Mercury, Nevada. RUTH, the Laboratory's first nuclear test, explored a new design for fission devices that offered hope for smaller, more efficient bombs and provided information about certain thermonuclear reactions. The experiment exemplified Livermore's commitment to be a "new ideas" laboratory. RUTH was fired on March 31, 1953-just six months after Livermore opened.
The device, Hydride I, weighed 7400 lb, was 56 inches in diameter and was 66 inches long. It was installed on a 300-ft tower, and Laboratory researchers stood back at the outlying observation station with their dark glasses on waiting for the device to go off. When it was fired, all that was visible was a small speck of light on the horizon-no mushroom cloud. Normally during a test, the detonation is seen about a minute before the sound reaches the observation station, and there is an announcement over the loudspeaker system warning to brace for the shock. According to Wally Decker, a young Laboratory engineer involved in his first field test, the shot went "pop." The predicted yield was 1.5 to 3 kt, while the 200 ton yield was a fraction of that. As the dust cleared, dismayed engineers and scientists peered through their field glasses and saw the tower was still standing. As Decker walked away he passed a guard who asked in all innocence, "When is the sound going to get here?"
While Livermore researchers were trying to find out what went wrong with the shot, Los Alamos personnel were busy taking a picture of the barely damaged tower. The Los Alamos contingency kidded Livermore about the shot, and even about the shipping boxes, which were painted a bright silver instead of the military olive drab that Los Alamos used.
A few months later the Laboratory prepared for another event with a slightly different design, and chose a 100-foot tower instead of a 300-foot one. Like Ruth, Livermore's second hydride test, Ray, on April 11, 1953, also fizzled. The explosion, however, at least managed to level the bomb's 100-tower. The tower had an open platform and the device was set up on a blustery day around Easter during rain, snow, and a dust storm. To protect the device from the weather, a large canvas tarpaulin was used to cover it. The device was fired with the same dismal results. The guard at the site commented, "Gee, you shouldn'tve put that canvas over it."
The research led to the Laboratory's first weapon-development assignments, including the W48 155-mm howitzer atomic projectile and other tactical nuclear weapon systems.
For the Livermore-designed weapon systems being retired the Lab has a continuing active responsibility to ensure safe and timely dismantlement and disposition of excess materials. In 1996, Livermore completed dismantlement of the W48 artillery projectiles, the W55 SUBROCs, and the W70 Lance warheads.
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