Day joined the
Royal Navy as a probationary
flight sub-lieutenant, and was confirmed in the rank of flight sub-lieutenant on 21 August 1915. He received the Royal Aero Club Aviators' Certificate No. 1949 after flying a
Caudron biplane at the Royal Naval Flying School,
Eastchurch, on 2 October 1915. He was first stationed aboard the
seaplane carrier , part of the
Harwich Force, where he gained a reputation as a skilled and daring flyer, and was promoted to flight lieutenant on 31 December 1916. Day chafed at the lack of activity at Harwich, and gained a transfer to the
light cruiser . Following her grounding in August 1917, he was posted to the experimental air station at
RNAS Kingsnorth on the
Isle of Grain. Day was already an experienced pilot when he joined No. 13 Squadron RNAS, based at
Dunkirk, on 19 December 1917. Between 3 January and 19 February 1918 he scored five victories while flying a
Sopwith Camel. According to his commanding officer's report: :"...He was shot down by six German aircraft which he attacked single-handed, out to sea. He had out-distanced his flight, I think because he wished to break the [enemy's] formation, in order to make it easier for the less experienced people behind him to attack. He hit the enemy and they hit his machine, which burst into flames; but, not a bit flurried, he nose-dived, flattened out, and landed perfectly on the water. He climbed out of his machine and waved his fellow-pilots back to their base; being in aeroplanes [not sea-planes] they could not assist him." A search was immediately launched, but no trace of him was found. ==Honours and awards==