On 26 February 1916, William Neilson Deas applied for total exemption from military service, stating: “I believe in the brotherhood of man and would rather sacrifice my own life than take anothers whatever his nationality. Further, I cannot conscientiously take part in any form of militarism as I consider such to be directly opposed to my convictions”
On 6 April 1914, he was granted exemption from combatant service only. He appealed but the appeal was dismissed. He was court-martialled in Edinburgh Castle and in Hamilton, where he was sentenced to 112 days hard labour at Berlinnie civil prison. He served his sentence there from 26 June 1916 to 4 October 1916. He was assigned to the home office scheme on 26 February 1917 in Wakefield.