Under the agreement 5.37 tonnes of UK-produced plutonium was sent to the US in exchange for 6.7 kg of tritium and 7.5 tonnes of HEU between 1960 and 1979. A further 470 kg of plutonium was swapped between the US and the UK for reasons that remain classified. Some of the UK-produced plutonium was used in 1962 by the US for the only known nuclear weapon test of reactor-grade plutonium. The plutonium sent to the US included some produced in UK civil Magnox reactors, and the US gave assurances that the civil plutonium was not used in the US nuclear weapons programme. It was used in civil programmes which included californium production and reactor research.