Lt/Cmdr J. H. C. Sykes joined the Fleet Air Arm in 1939 and trained as a pilot, but due to a shortage of qualified RAF pilots, he joined RAF Fighter Command.
John joined 64 Squadron at Kenley on the 8 July 1940 and served with it until September 15, when he was transferred back to the Fleet Air Arm.
John later converted to RAF Hurricanes and was part of the Royal Navy Fighter Squadron, which took part in operations in the Western Desert.

During 1942, John served in the Far East flying Fulmars.

Post war, he was loaned to the Australian Navy to help set up their air component.