Percy was born on 9 October 1894 in Basford, Nottinghamshire the first child of Robert and Sarah (née Potter) Duffield, with three sisters and a brother, Ethel (1898), Florence (1901), Grace (1902) and Robert H (1911) making up the family unit. With the father a coal miner the family moved to where the work was available in Nottinghamshire, Yorkshire and Wales before returning to Basford in retirement. Percy swapped the coal mines of Wales to join the Royal Navy in 1913.

Percy joined the Royal Navy on 28 March 1913 when he joined HMS VIVID II, the Royal Naval Barracks in Devonport, when he was 18 years and 4 months old, and became a Stoker Second Class. On 16 September 1913 joined HMS EXMOUTH and on board was advanced to Stoker First Class on 28 March 1914 before returning to VIVID II on 23 May 1914. On 9 June he joined HMS SKIRMISHER for 4 months before joining HMS DOLPHIN on 5 October 1914. He was drafted to HMS MAIDSTONE on 4 December 1914 with a draft back to DOLPHIN on 7 September for 2 weeks and a return to MAIDSTONE for E18 on 27 September 1915.

E18 was a unit of the 8th Submarine Flotilla based in Harwich with MAIDSTONE as her depot ship. E18 was part of the 8th Flotilla that was despatched to the Baltic in 1915 to be based in Reval (now Tallin), Estonia, using  a Russian depot ship the DVINA. She departed Reval on the 25 May for her 7th Baltic Sea patrol in company with E8, separating on the 26 May for designated patrol areas. E18 was in action on the afternoon of the 26 May and her last sighting was on 1 June but she failed to return to Reval as programmed. Her resting place has been located and the wreck survey showed hatches open and damage on the underside of the hull indicating she had hit a mine while in surface transit. She was declared lost on the 11 June after failing to return to Reval.

Percy Duffield,  Sto 1c,  Svc No. K18506 aged 21 years and 4 months had “Crossed The Bar” with 29 of his shipmates.