 In 1916, Inglis was placed in charge of bridge design and supply at the War Office in which role he was a proponent for the increased use of girder bridges in military applications. It was Inglis that first proved to the army that the heavy components essential to girder bridges did not prevent their rapid assembly in field conditions. This led to the greater use of such bridges, particularly the Inglis Bridge, for tanks later in the war. He received promotion to the rank of captain on the General List of Officers on 6 May 1916 and became a staff captain attached to the War Office on 26 June 1917. He was promoted to the brevet rank of major as part of the King's Birthday Honours on 3 June 1918 and later that year worked with Giffard Le Quesne Martel to develop some of the earliest bridgelaying tanks. Inglis retired from the army on 9 March 1919, having been rewarded for his military service with an appointment as an Officer of the Order of the British Empire.
