Orange Herald

However, due to its size it was not suited as a warhead for the ballistic missile and was more of an insurance which could be used if other devices failed to achieve the desired yield.

As a result, the UK wanted to demonstrate its ability to manufacture megaton class weapons by proof-testing them before any legal prohibitions were in place.

According to an article in New Scientist, Prime Minister Harold Macmillan was also hoping to convince the US to change the McMahon Act, which prohibited sharing information even with the British, by demonstrating that the UK had the technology to make a thermonuclear weapon (an H-bomb), and he put William Penney, a British professor who had worked in the Manhattan Project, in charge of developing this bomb.

[6] It is believed by some that the large requirements of tritium that Orange Herald needed (actually it contained only a small amount of thermonuclear material[2]) was a major cause of the Windscale fire.

One of the workers in the British nuclear program, Dr. Bryan Taylor, is quoted as saying "I thought that Orange Herald was a stupid device.