| Harold Day | |
| Birth Date: | 1897 4, df=yes |
| Birth Place: | Abergavenny, Wales |
| Death Place: | Vicinity of Harnes, France |
| Placeofburial: | St. Mary's A.D.S Cemetery, Haisnes, Pas de Calais, France |
| Allegiance: | United Kingdom |
| Branch: | Royal Navy |
| Serviceyears: | 1917–1918 |
| Rank: | Flight Sub-Lieutenant |
| Unit: | No. 10 Squadron RNAS No. 8 Squadron RNAS |
| Awards: | Distinguished Service Cross |
Flight Sub-Lieutenant Harold Day (17 April 1897 – 5 February 1918) was a Welsh World War I flying ace credited with 11 confirmed aerial victories.[1]
Day was the son of William John and Elizabeth Day, of Wernddu, Abergavenny, Monmouthshire.[2] He joined the RNAS as a probationary temporary flight officer, and was commissioned as a temporary flight sub-lieutenant on 30 June 1917.
He first served in No. 10 Naval Squadron, flying a Sopwith Triplane. He scored his first aerial victory with them, sending an Albatros D.V down out of control on 12 August 1917. He was then posted to No. 8 Naval Squadron and flew the Sopwith Camel for his remaining ten victories. During December 1917, he teamed with Guy William Price to drive down DFW two-seater reconnaissance aircraft on three different days. Fighting solo, Day destroyed one enemy aircraft and drove down three others during January 1918. On 2 February 1918, he joined Robert J. O. Compston and three other RNAS pilots in destroying a German reconnaissance aircraft, and in driving down an Albatros D.V later in the day. On 5 February, he joined three other RNAS pilots in destroying a reconnaissance machine; that brought his total to one enemy aircraft destroyed solo, two more shared, and eight driven down out of control. He then dived on another German aircraft.[1] Day's Camel came to pieces during the dive, plummeting him to his death.[3] Günther Schuster of Jasta 29 was credited with the victory.[1]
Day was awarded the Distinguished Service Cross, which was gazetted on 22 February 1918.
He is buried at St. Mary's ADS (Advanced Dressing Station) Cemetery, Haisnes, France.[2]