Kenneth Gilbert Hubbard was born in Norwich in Norfolk on 26 February 1920, the son of Gilbert Claud Hubbard, a mechanical engineer and professional Association football player who played for Norwich City, and his wife Florence Dack. He was educated at Norwich Technical College from 1932 to 1935, where he trained as a draughtsman. He then worked as a draughtsman for Stevensons of Norwich.
After the outbreak of the Second World War, Hubbard joined the Royal Air Force on 21 June 1940. He earned his wings at No. 2 Flying Training School RAF at RAF Brize Norton, and was commissioned as a pilot officer in May 1941. He was posted to No. 2 Central Flying Training School at RAF Cranwell in June 1941, and then to No. 12 Flying Training School RAF at RAF Grantham in July 1942 as an instructor. In December 1942 he was posted to 311 Ferry Training Unit at Moreton in Marsh, where he did a conversion course on the Vickers Wellingtonmedium bomber. He flew one out to Foggia Airfield Complex in Italy in January 1944, and joined No. 70 Squadron RAF, which operated the Wellington. He was awarded the Distinguished Flying Cross on 20 April 1945. His citation noted that he had "taken part in many attacks in close support of the Fifth and Eighth armies and against marshalling yards in the Po valley. One night in May 1944 he participated in a special low-level attack on an important railway bridge in north Italy." From January to May 1945 he was a pilot instructor at RAF Qastina in Palestine. He then returned to No. 70 Squadron RAF in Italy, which was now flying B24 Liberator bombers from Tortorella.
No. 49 Squadron was assigned to Air Vice Marshal Wilfrid Oulton's Operation Grapple Task Force to conduct nuclear tests at Christmas Island in the Pacific Ocean as part of the British hydrogen bomb programme. No 49 Squadron had eight Valiants, but only four deployed: XD818, piloted by Hubbard, now a Wing Commander; XD822, piloted by Squadron Leader L. D. Roberts; XD823, piloted by Squadron Leader Arthur Steele; and XD824, piloted by Squadron Leader Barney Millett. The other four Valiants remained at RAF Wittering, where they were used as courier aircraft for bomb components. The first mission was flown by Hubbard in XD818, with Millett and XD824 as the "grandstand" observation aircraft. The bomb was dropped from off the shore of Malden Island at 10:38 local time on 15 May 1957. Hubbard missed the target by just. He became the first British pilot to drop a live hydrogen bomb. The bomb was a failure; its yield was estimated at, far below its designed capability. Hubbard and his four crew members were awarded the Air Force Cross in the 1957 Birthday Honours. His aircraft, Vickers Valiant XD818 is now on display in the Royal Air Force Museum at RAF Cosford. After the Grapple tests Hubbard served at HQ RAF Bomber Command from 1959 to 1961. He was promoted to group captain, and commanded RAF El Adem in Libya. In 1963, he assumed command of RAF Scampton, the base of the Avro Vulcan bombers of Nos 27, 83 and 617 Squadrons RAF equipped with the Blue Steelstandoff missile. His final appointment was Group Captain Training at HQ RAF Transport Command. He retired from the RAF in 1966.
Later life
In retirement, Hubbard tried his hand at farming in the West Country. The venture was unsuccessful, but he did meet Margaret Grubb, whom he married at the register office in Blyth, Suffolk, on 14 March 1975, and he moved to Margaret's home at Blythburgh Priory in Suffolk. Members of 49 Squadron serving during the Grapple nuclear test series formed a Megaton Club and with Hubbard as its President, and they met annually at the Royal Air Force Club at 128 Piccadilly in London. In 1974, Hubbard became Director of Sales and Marketing of the Vehicle Air Conditioning Division of his cousin Geoffrey Hubbard's Hubbard–Reader Group of refrigeration engineering companies. He retired in 1982. He chaired the local review committee for parole at HM Prison Blundeston, and was involved with the local Air Training Corps and the RAF Benevolent Fund. His wife died in 1997. He had no children from either of his marriages. With Michael Simmons, a director at Hubbard engineering, he wrote a book about his experience as the commander of No. 49 Squadron in Operation Grapple. The book was published by Ian Allan in 1985 under the title of Operation Grapple. A new edition with a different title of Dropping Britain's First H-Bomb was published by Pen and Sword in 2008. He died in Blythburgh on 22 January 2004.