Chapman joined the Royal Marines on 26 September 1934 at the Depot RM, Deal. His Regimental Number was: Chatham/X1047. After a number of miscellaneous drafts and gunnery courses he was promoted to Corporal on 8 June 1937 before being drafted to HMS Sheffield, a Town class cruiser, on 24 August 1937, the day the ship was first commissioned. In September 1938 he joined HMS Royal Sovereign, a Revenge class battleship and volunteered for flying training.

On 1 May 1939 he was transferred to the RN on probation as an Acting Leading Seaman to commence pilot training on No 4 Naval Pilots Course. Other Royal Marines on his course were; Lieutenants Cheesman, Jolliffe, Marryat and Wright, Corporals Jaggard, Lyall and Yarde (the latter did not qualify). His Elementary Flying Training took place at Rochester before graduating to No 7 FTS at Peterborough. Chapman completed his flying training on 3 December 1939 and was promoted to Acting Petty Officer Airman the next day; his FAA number was FX 82597.

Immediately Chapman commenced seaplane training at  RNASs Lee-on-Solent, Donibristle and Ford after which he was posted to 771 Squadron, RNAS Hatston, as a Walrus pilot from 30 March 1940 until 31 October 1941 and during that period was confirmed in the rank of PO Airman. Chapman returned briefly to Lee-on-Solent in November 1941 to join 764 Squadron and during that month was lent for two weeks to RNAS Sandbanks, at Poole, which, as the Royal Motor Yacht Club, had been requisitioned as one of RNAS Lee-on-Solent's satellite air-sea rescue seaplane bases. He was then detached to HMS Skirmisher, a Coastal Forces Base at Milford Haven for a month before joining HMS Pegasus, the Seaplane Training Ship.

Tragically, on 6 February 1942 Chapman was killed “hooking on”. There was no accident report but it is believed this refers to the procedure for “hooking on” the Walrus to the ship's crane before being hoisted back on board. He was buried in Kilbride Old Churchyard, Lamlash, Isle of Arran.