W9 / Mk.9

W9 T-124 280mm AFAP

Steps were also taken to develop Army weapons capable of delivering atomic weapons on the battlefield. The first weapon to appear was the mammoth 280mm gun. Since the 280mm gun had already been designed, the major developmental problem was evidently the design of a stable, rugged and relatively small atomic round that could be fired by the artillery. With reductions in size and an increase in the variety of yields, production of such a round soon became possible.

A live test of the Mk-9 fired from the 280mm cannon was the 15-kiloton GRABLE test conducted on May 25, 1953, as part of Operation Upshot-Knothole. A single test shot was fired seven miles at the Nevada Test site. The Army successfully fired an atomic shell from the World War II vintage 280mm gun, which detonated 160 meters above ground. The resulting 15 kt GRABLE explosion not only symbolized the addition of an awesome new weapon to the Army's arsenal, but also symbolized the true beginning of the atomic era for the Army. This shot was the first detonation of a gun-type atomic bomb since the bombing of Hiroshima on 06 August 1945.

Operation Upshot-Knothole at the Nevada Test Site consisted of 11 atmospheric tests. There were three airdrops, seven tower tests, and one airburst. Operation Upshot-Knothole drew a great deal of criticism as resultant fallout levels produced increased offsite radiation exposures. About the time (afternoon of 26 May 1953) the GRABLE debris cloud segment stretched between the 5.6 and 9.2 km trajectories was carrying the higher portion of the radioactive cloud across the east coast (over Maryland), a violent hail storm occurred at Washington, D.C. Hailstones collected from this storm were tested by the U.S. Naval Research Laboratory there (Blifford et al. 1953) and were found to contain high concentrations of radioactive fission products, particularly high in their centers. High concentrations of radioactivity were also found in the air near the surface, undoubtedly carried to the ground by strong vertical air currents associated with the thunderstorm.

Mk.9 T-4 Atomic Demolition Munition