William was born on 4 July 1914 in St Pancras, London to Walter and Louise née Machin, a Christian family. William was baptised in St Mary Magdalene Church in St Pancras. His father Walter was killed in 1916 serving in the Army in WW1.

William converted to Judaism to marry Dora Levy in 1937 and their first child Doreen was born in 1938. In 1939, the family were living at 242 Hedge Lane, Edmonton where William was working as a boot and shoe salesman. Their son Phillip was born in 1941 two months before William’s death.

William was an air gunner on Wellington R1728 which departed RAF Steeple Morden on a night navigation training exercise. The aircraft was reported missing and was thought to have crashed into the North Sea. Four of the aircrew lost their lives in the crash. The four airmen who lost their lives in the crash were:

Flying Officer William Foster
Pilot Officer Charles Bristow
Sergeant Leonard Parry
Sergeant Edward Buckingham.

The other two members of the aircrew, William and RCAF Sergeant Richard Percy Burt managed to launch an inflatable dinghy. On 21 June, thirteen days later, the Royal Navy Liaison Officer at Humber advised that a dinghy containing the bodies of Sgt Hare and Sgt Burt had been recovered by an RAF high speed launch.