S/Ldr. Assheton was born on 12th December 1917.
He joined the RAF with a short service commission in early 1939.

William was posted to 222 Squadron at Duxford in early November 1939.
In August, the squadron was stationed at Hornchurch, and on 30th of that month, William crash-landed his Spitfire R6720 at Bekesbourne aerodrome after combat over Canterbury.
On 11th September, William forced-landed Spitfire R6638 on Parsonage Farm, Fletching, after an action over Maidstone.

William's third escape came just before midday on 20th September when he baled out, with slight burns, after being shot down in a surprise attack by BF 109s over the Thames Estuary. He landed at Latchingdon and was admitted to St. Peter’s Hospital, Maldon. His aircraft, Spitfire K9993, crashed and burned out at Linkhouse Farm, West Hanningfield.

In 1945 William was awarded the DFC (10th April 1945) for service with 540 Squadron, a mosquito photographic-reconnaissance unit.

William Assheton remained in the RAF after the war, graduated from the RAF Staff College and retired on 22nd November 1957, as a Squadron Leader.