Violet Club - Conclusion

Conclusion

These very large and dirty fission bombs were the largest pure-fission bombs deployed by any state, and unlike their predecessors, Blue Danube and Red Beard, they used HEU as a fissile material rather than plutonium, the reason being primarily economic. The cost of HEU to the Royal Air Force was (at 1958-9 prices) £19,200 per kg, with plutonium priced at £143,000 per kg. Although a HEU weapon needed more fissile material for a given yield than a plutonium weapon, a saving per weapon was of the order of £22.7M at 2006 prices. Thirty-seven Green Grass warheads were built (five as Violet Club) saving the Treasury £840M. The influence of the Treasury on weapons procurement should not be underestimated: it reaches even into weapons design. Clearly, there were economic benefits in building large and dirty U-235 fission bombs, rather than cleaner, but more expensive plutonium weapons, especially given the shortage of plutonium. By 1958 Britain's accumulated production of plutonium was only 472.2 kg and a proportion of that was bartered to the United States in exchange for HEU and other items. Up to 1958, British output of HEU was only 860 kg, while the United States supplied the UK with approximately seven tons of HEU from their less costly production process. So HEU used for Green Grass was purchased cheaply from the U.S. while selling to the U.S. the unwanted and high-priced weapons-grade plutonium.

Knobkerry, alias Green Grass, alias Interim Megaton Weapon, alias Violet Club and Yellow Sun Mk.1 had one other distinction. It was the last entirely British nuclear weapon deployed with the UK Armed Services. The British Operation Grapple thermonuclear weapon tests at Christmas Island in 1957-58 were the end of evolution. There were no more wholly home-grown designs. Britain never deployed a true thermonuclear weapon of wholly home-grown design. All the weapons tested at Operation Grapple were abandoned, because AWRE no longer needed them; although some of their features were undoubtedly incorporated into later weapons. These Granite-type devices were all experimental devices needing to be developed further into reliable Service-engineered warheads at considerable cost in time and money. The U.S. designs offered after 1958 were fully tested and engineered, and cheap to produce. They were manufactured in Britain from British materials and U.S. blueprints. They were British property and there were no American political constraints on their use; they were also a favourable deal for the Treasury; and Violet Club and Yellow Sun Mk.1 bridged the gap until the American designs could be manufactured.