In 1914 Robb along with his battalion was mobilised for war and is recorded as entering the theatre of operations (i.e. France) in April 1915. He was awarded the Military Cross whilst serving with the Northumberland Fusiliers. Whilst on the Western Front with his unit Captain Robb was recorded as an active and popular member of the 4th Battalion the Northumberland Fusiliers. He was even given temporary lieutenant colonel rank and commanded the battalion in the Battle of St Quentin on 21 March 1918; during this particularly fierce battle he was wounded and evacuated.