Born in Latchford and raised near Porquis Junction, Cosens enlisted in the Argyll and Sutherland Regiment, Canadian Active Service Force, in 1940 and transferred to the Queen's Own Rifles of Canada in 1944. Early on February 26, 1945, his unit attacked German forces at Mooshof, Holland, a strategic position vital to the success of future operations. His platoon suffered heavy casualties and Cosens assumed command. Supported by a tank, he led another attack against three enemy strongpoints, which he captured single-handed. He later was killed by a sniper. For his "outstanding gallantry, initiative and determined leadership" he was posthumously awarded the Commonwealth's highest decoration for valour, the Victoria Cross.