 He was awarded the Distinguished Service Order for his gallantry at Lone Pine, his part in the capture of Pozières, and his role in repelling a German counterattack at Mouquet Farm, near Pozières.Mackay held the temporary position of commander of the 1st Infantry Brigade in January 1917, for the first of what would be five times totalling 92 days in 1917.He commanded the 4th Infantry Battalion in the advance to the Hindenburg Line, including the capture of the fortified town of Hermies.