He was commissioned as a second lieutenant in April and was given five days' leave in London to acquire an officer's uniform and equipment. On his return, he was assigned to 4 Squadron and on 7 July transferred to 15 Squadron, still flying in the B.E.2. On 21 July Barker claimed a Roland scout "driven down" with his observer's gun, and in August claimed a second Roland, this time in flames. He was Mentioned in Despatches around this time. He officially qualified as an Observer on 27 August and on 15 September he worked for the first time with Canadian troops, including his old regiment. On 15 November, Barker and his pilot, flying very low over the Ancre River, spotted a large concentration of German troops massing for a counter-attack on Beaumont Hamel. The crew sent an emergency Zone Call which brought to bear all available artillery fire in the area onto the specified target. The force of some 4,000 German infantry was effectively broken up. He was awarded the Military Cross for this action in the concluding stages of the Battle of the Somme.