Slater transferred to the Royal Flying Corps in 1915 and served in France with 18 Squadron as an observer. After pilot training, he was posted to 1 Squadron where he scored his first two victories flying the Nieuport scout. Later, he was posted to 64 Squadron and scored 22 more victories by the end of May 1918. He was posted to the Home Establishment in July 1918 and served as an instructor until the war ended. Slater remained in the Royal Air Force and was killed in a crash at Upavon in 1925.
Military Cross (MC)
"T./2nd Lt. (T./Capt.) James Anderson Slater, Gen. List and R.F.C.
For conspicuous gallantry and devotion to duty. When returning from a patrol he attacked enemy infantry, silenced a field gun and fired on transport. On another occasion he silenced a battery in very difficult weather conditions, fired on ammunition wagons and enemy infantry, and brought back his patrol safely. He also led a patrol of twelve machines in very bad weather to attack a wood held by the enemy. His patrol dropped over thirty bombs, fired 3,000 rounds and drove the enemy from the wood with heavy casualties. In the course of this flight six enemy scouts were engaged and driven off. Later, he led a similar patrol with great success. He showed splendid courage and determination."
Supplement to the London Gazette, 5 July 1918 (30780/7924)
Military Cross (MC) Bar
"T./Capt. James Anderson Slater, M.C., Gen. List, and R.F.C.
For conspicuous gallantry and devotion to duty. On one occasion during the recent, operations he attacked a large formation of hostile scouts, one of which he drove down in flames. Later, during the same flight, he took part in a general engagement, in which he drove down another enemy machine completely out of control. Two days later he attacked two enemy scouts, causing one of them to crash to earth. In eighteen days he has engaged in twenty-five combats at close quarters, shooting down eight hostile machines. His great gallantry and fine offensive spirit have inspired all ranks to a very high degree.
(M.C. gazetted 4th February, 1918.)"
Supplement to the London Gazette, 22 June 1918 (30761/7400)
Distinguished Flying Cross (DFC)
"Lt. (T./Capt.) James Anderson Slater, M.C.
This officer has led numerous offensive patrols with the utmost skill and determination, and it is entirely due to his fine leadership that many enemy aircraft have been destroyed with the minimum of casualties to his formation."
Supplement to the London Gazette, 3 August 1918 (30827/9204)