Land Rover entered production in 1948 with what was later termed the Series I. This was launched at the Amsterdam Motor Show. It was originally designed for farm and light industrial use, and had a steel box-section chassis, and an aluminum body. Originally based on the US Army Jeep the Land Rover was a single model offering, which from 1948 until 1951 used an 80 in wheelbase and a 1.6-litre petrol engine producing around 50 bhp. The 4-speed gearbox from, the Rover P3 was used, with a new 2-speed transfer box. This incorporated an unusual 4-wheel drive system, with a freewheel unit. This disengaged the front axle from the manual transmission on the overrun, allowing a form of permanent 4WD. A ring-pull mechanism in the driver's footwell allowed the freewheel to be locked to provide more traditional 4WD. This was a basic vehicle, tops for the doors and a roof (canvas or metal) were optional extras. In 1950, the lights moved from a position behind the grille to protruding through the grille.