Georges Guynemer, France’s greatest ace, told SPAD designer Louis Béchereau that the 150 hp SPAD S.VII was no longer a match for the latest German scouts. Béchereau responded with the S.XIII, a larger, stronger airframe built around the geared 200 hp Hispano-Suiza 8B V-8 engine. The prototype flew on 4 April 1917; production aircraft reached the front by May. The S.XIII was fast—211 km/h at 1,000 metres—and structurally robust in a dive, but its left-handed propeller and high wing loading made it difficult to land. It carried two forward-firing Vickers machine guns, each with 400 rounds, and it could out-run anything in the German inventory. By the Armistice, 8,472 had been built, with orders for another 10,000 cancelled. Nearly every French fighter squadron flew it, and the United States Army Air Service adopted it as their primary fighter after the Nieuport 28 proved structurally suspect. Fifteen of the sixteen American fighter squadrons were equipped with the SPAD. Aces such as Guynemer, René Fonck, Frank Luke, and Eddie Rickenbacker scored heavily in the type. Guynemer’s last victories were scored in the SPAD XII in July 1917, by which time the S.XIII had been in front-line service since May and other pilots had already been credited with victories in the type. It was not a gentle machine, but it was a war-winner—fast, tough, and relentless.