At the 1950 Isle of Man TT Armstrong came sixth in the Senior TT on a Velocette. He came sixth in the 500 cc class, and seventh in the 350 cc class for the 1951 Grand Prix World Championship, and was then offered a place for the 1952 season on the Norton team. Armstrong won his first ride for Norton, the 500 cc class in the Leinster 200. He then won the German Grand Prix, and the Isle of Man Senior TT. It was Armstrong's most successful season so far, coming third in the 500 cc 1952 World Championship, and second in the 350 cc.