Adair fought in the
First World War. He joined the
British Army, receiving his
commission as a probationary
second lieutenant on 2 May 1916 in the 5th (Reserve) Battalion of the
Grenadier Guards, the same regiment with which an ancestor of Adair's had been serving when he was killed at the
battle of Waterloo. From January 1917 onwards he served in the
trenches of the
Western Front in France and Belgium as part of the 2nd Company, 3rd Battalion, Grenadier Guards, with the rank of
lieutenant. The battalion was part of the
2nd Guards Brigade of the
Guards Division. Adair's first major battle was in the pursuit of the retreating
German Army to the
Hindenburg Line. The division then took part in the
battle of Passchendaele. Adair, however, took no part in the battle, due to an injury sustained in a bicycle accident in early July 1917. He returned to the battalion in January 1918, by which time he discovered that there were only four of his fellow officers still with the battalion. Adair was awarded his first
Military Cross (MC) on 2 December 1918. The citation reads: With the
acting rank of
captain, Adair was
Officer Commanding 2 Company from 22 September to 11 November 1918, receiving his second MC after the war on 2 April 1919 "for conspicuous gallantry and skill at
Preux-au-Sart, on 4 November 1918. In command of the left front company, which was held up by an organised line of machine guns, he so manoeuvred his platoons as to capture the line with a minimum of casualties. Although wounded in the leg, he continued in command until relieved the following day". ==Between the wars==