I have undertaken further research on my father's involvement in Grapple Y.
His log books reveal that he travelled to Christmas Island arriving on 25 April 1958 following a three-day mixed commercial/military flight combination via Goose Bay, New York, San Francisco and Honolulu. The airburst weapon known as Dickens was exploded on April 28 just south of CI and yielded 3 megatons. He flew home on the reverse route the following day. His logbook has no entries covering his time on the island. Why was he there? What was so important that he was required to spend 6 days travelling for three days on CI? I will probably never know since he died of multiple carcinomas in 1985.
An account of Operation Grapple Y by Susie Boniface in a Mirror Special Report includes harrowing detail of one pilot's involvement in the tests as 'sniff 2' and his most unfortunate legacy. You may find this very upsetting.The Damned: Chapter 3 - Operation Grapple RB