Operation Grapple - Grapple X

Grapple X

Following the disappointing results of the first Grapple trial, Grapple X was conducted at Christmas Island. For Grapple X, the bombs were exploded over Christmas Island instead of over Malden Island to save time and money.

With the experience and knowledge gained from the first Grapple tests, the weaponeers had developed a new H-bomb design with a 50 percent more powerful fission primary stage and a simplified thermonuclear secondary. Grapple X was dropped and detonated over the southern end of Christmas Island on November 8, 1957. The two-stage thermonuclear bomb exploded with a yield of about 1.8 megatons. This was close to being the real hydrogen bomb Britain wanted, but used a relatively large quantity of (expensive) highly enriched uranium.

The explosion did some damage to the island, resulting in some demolished and damaged military buildings. This damage was due to the higher-than-expected yield of the explosion.

Grapple X was spectacularly successful, exceeding its predicted yield of one megaton by about 80 percent. The U.K. had become an actual thermonuclear power with the detonation of Grapple X.