The next test was Grapple 2, of Orange Herald, the first British weapon to incorporate an external neutron initiator. It was dropped on 31 May, and exploded with a force of . The yield was the largest ever achieved by a single stage device, which made it technically a megaton weapon. The bomb was hailed as a hydrogen bomb, and the truth that it was actually a large fission bomb was kept secret by the British government until the end of the Cold War. Penney cancelled the planned Green Granite test, and substituted Purple Granite, a Short Granite with some minor modifications. Its yield was a very disappointing , even less than Short Granite; the changes had not worked.