Joining the army before the war, Winkler served with the Lothian and Border Horse Yeomanry as a trooper before he transferred to the Army Service Corps as a driver. In March 1915, he was gazetted to the Royal Garrison Artillery as a Second Lieutenant. After serving in France, he transferred to the Royal Flying Corps in August 1916, becoming a pilot in February 1917. Two months later, Winkler was assigned to 48 Squadron as a Bristol Fighter pilot. In less than a month, he and his observer, Ernest Moore, were credited with six Albatros D.IIIs before they were shot down near Gavrelle by Lothar von Richthofen and Leutnant Wilhelm Allmenröder of Jasta 11. Crashing just 300 yards beyond the British lines, Winkler and Moore were captured by the Germans.