United States and the "Marathon" Superbeetle in the rest of the world. It featured unique "Marathon Blau" metallic blue paint, steel-pressed 10-spoke magnesium-alloy wheels, a commemorative metal plate mounted on the glovebox and a certificate of authenticity presented to the original purchaser. Dealer-installed options for this limited-edition Superbeetle included the following: white stripes running the length of the rocker-panel, a special shifter knob, bumper overriders, tapered exhaust tips, fake walnut inserts in the dashboard (behind the steering wheel and the glovebox cover) as well as Bosch fog lights mounted on the front bumper. 1961–1973: Beetle to Golf The 1961 Type 1 Beetle had a 36 hp 1200cc four cylinder air-cooled flat-four opposed OHV engine made of aluminium alloy block and heads. By 1966, the Type 1 came with a 1300cc engine. By 1967 the Type 1 had a 1500cc engine, and 1600cc in 1970. The air-cooled engine lost favour in the United States market with the advent of unleaded petrol and smog controls. These air-cooled engines were commonly tuned to be fuel-rich in order to control engine over-heating, and this led to excessive carbon monoxide emissions. VW production equipment was eventually moved to Mexico where vehicle emissions were not regulated. Beetles were popular on the US West Coast where the limited-capacity cabin heating was less inconvenient. Beetles were popularised on the US West Coast as beach buggies and dune buggies. VW expanded its product line in 1961 with the introduction of four Type 3 models (Karmann Ghia, Notchback, Fastback, and Variant) based on the new Type 3 mechanical underpinnings. The name 'Squareback' was used in the United States for the Variant. In 1969 the larger Type 4 (411 and 412) models were introduced. These differed substantially from previous vehicles, with the notable introduction of monocoque/unibody construction, the option of a fully automatic transmission, electronic fuel injection, and a sturdier powerplant. In 1964, Volkswagen acquired Auto Union, and in 1969, NSU Motorenwerke AG (NSU). The former company owned the historic Audi brand, which had disappeared after the Second World War. VW ultimately merged Auto Union and NSU to create the modern Audi company, and would go on to develop it as its luxury vehicle marque. The purchase of Auto Union and NSU was a pivotal point in Volkswagen's history, as both companies yielded the technological expertise that proved necessary for VW to survive when demand for its air-cooled models went into