He joined the Royal Scots as a machine gunner and later became an officer in the then new branch of the service, the Tanks Corps. While serving with the tanks he was caught in a mustard gas attack and lost his eyesight, but later he regained sight in his right eye.
The winner of many amateur golf events in Europe as well as the French Open, Armour came to the United States soon after the war ended and turned professional in 1925. In 1927 he won the U.S. Open Championship and the Canadian Open. Subsequently he went on to win every major championship: the British Open; the P.G.A.; the Western; the Metropolitan; and too many cash-prize tournaments to attempt to list.
In 1929 he took over the post of golf professional at the Boca Raton Club, in Florida, where over the next quarter of a century his instruction ranged prom teaching duffers how to break 100 to brushing up the games of the top tournament professionals when they couldn't iron out their own difficulties. Armour always claimed that the instructional part of his golf career was the best -- the part he enjoyed the most.