In 1932, Ferdinand Porsche produced prototypes for the NSU company of Germany which eventually led to the design of the Volkswagen. The prototypes had a rear mounted, air-cooled engine, torsion bar suspension, and the spare tire mounted at an angle in the front luggage compartment. In 1936, Porsche produced three Volkswagen prototypes, one of which was a 995 cc, horizontally opposed, four cylinder automobile. Passenger car development was sidetracked during World War II, when all attention was on military vehicles. In 1945, Volkswagen production began and 1,785 Beetles were built. The Volkswagen convertible was introduced in 1949, the same year that only two Volkswagens were sold in the United States. 1950 marked the beginning of the sunroof models and the transporter series. The Karmann Ghia was introduced in 1956, and remained in the same basic styling format until its demise in 1974. The 1500 Squareback was introduced in the United States in 1966 to start the Type 3 series. The Type 4 was imported into the U.S.A. beginning with the 1971 model. 1977 marked the last year for the Beetle. The Beetle convertible was available through 1980 and the new VW bus, the Vanagon, was introduced in 1980.