In 1957 the Operation Grapple tests were carried out. The first test, Green Granite was a prototype fusion bomb, but failed to produce equivalent yields compared to the U.S. and Soviets, achieving only approximately . The second test Orange Herald was the modified fission bomb and produced —making it the largest fission explosion ever. At the time almost everyone (including the pilots of the plane that dropped it) thought that this was a fusion bomb. This bomb was put into service in 1958. A second prototype fusion bomb Purple Granite was used in the third test, but only produced approximately .