The big breakthrough was the launch in 1948 of the XK120 sports car, with the new XK twin overhead camshaft (DOHC) 3.5 litre hemi-head six-cylinder engine designed by William Heynes, Walter Hassan and Claude Baily. This engine had been designed during the long nights during the war when they would be on fire watch in the factory. After several attempts a final design was arrived at. That is until owner William Lyons said "make it quieter". The car had originally been intended as a short production model of about 200 vehicles as a test bed for the new engine until its intended home, the new Mark VII saloon, was ready. The XK120's reception was such that production continued until 1954; it was followed by the XK140, the XK150, and the E-Type, keeping Jaguar in the sports car market.