'For conspicuous gallantry and devotion to duty. During the operations near Esnes on the 8th October 1918 Lance Corporal O'Brien was in command of a Lewis gun section. Throughout the advance of three miles he displayed great coolness in passing through enemy barrages, and kept well in hand his men, half of whom had never been previously under fire. When his Company had taken its objective, heavy machine gun and rifle fire was opened on its left flank by a party of from 40 to 50 of the enemy, when this NCO on his own initiative rushed his Lewis gun across to the exposed flank of is Company and by his fire inflicted such casualties on the enemy that they were forced to retire.'
Source: London Gazette
Date: 14 May 1919