When the First World War broke out in August 1914 Farrar was on holiday in England. He returned to South Africa and volunteered to serve against Germany. He was appointed assistant quartermaster-general to the South African forces that landed at Luderitz in Namibia (then occupied by Germany). He was charged with clearing the Luderitz-Keetmanshoop railway line that had been damaged by German colonial soldiers, as they retreated into the interior. Farrar got damaged boreholes at Garub between Luderitz and Kubis working to provide 150,000 gallons of water a day for South African troops. Farrar was killed on 19 May 1915 when his railway inspection car collided head first with a train.