The Defender was not an entirely new model at launch. It used engines and body panels carried over from the Series III Land Rover; gearbox, axles and suspension from the Range Rover.
Production of the model now known as the Defender began in 1983 as the Land Rover One Ten, a simple name which reflected the 110 inch (2.794 m) length of the wheelbase. The Land Rover Ninety, with 93inch (2.362m) wheelbase, and Land Rover 127, with 127in (3.226m) wheelbase, soon followed.
Outwardly, there is little to distinguish the post-1983 vehicles from the Series III Land Rover. A full-length bonnet, revised grille, plus the fitting of wheel arch extensions to cover wider-track axles are the most noticeable changes. Mechanically the Ninety and One Ten were a complete modernisation of the former Series platform. Specifically:
- The use of coil springs, whereas Series vehicles had leaf springs. This gave a more comfortable ride and improved axle articulation.
- A permanent four-wheel drive system as used since 1970 on the Range Rover, featuring a two-speed transfer gearbox with a lockable centre differential.
- As part of the update, a new series of progressively more powerful and more modern engines were designed, although the Series III engine line-up remained in place when the vehicles were first launched.
- The interior was modernised; a taller one-piece windscreen replaced the split-screen of the Series models.
The One Ten was launched in 1983, and the Ninety followed in 1984. From 1984, wind-up windows were fitted (Series models and very early One Tens had sliding panels), and a 2.5-litre, 68hp (51kW) diesel engine was introduced. This was based on the earlier 2.3-litre engine, but had a more modern fuel-injection system as well as increased capacity. A low compression version of the 3.5-litre V8 Range Rover engine was available too which transformed performance.
This period saw Land Rover market the utility Land Rover as a private recreational vehicle. Whilst the basic pick-up, Station Wagon and van versions were still working vehicles, the County Station Wagons were sold as multi-purpose family vehicles, featuring improved interior trim and more comfortable seats. This change was reflected in Land Rover starting what had long been common practice in the car industry - detail changes and improvements to the County model from year to year in order to attract new buyers and to encourage existing owners to trade in for a new vehicle. These changes included different exterior styling graphics and colour options, and a steady trickle of new "lifestyle" accessories that would have been unthinkable on a Land Rover a few years ago, such as radio/cassette players, styled wheel options, headlamp wash/wipe systems and new accessories such as surfboard carriers and bike racks. The switch from leaf- to coil spring suspension was crucial to the new models' success. It offered improved off-road ability and load capacity for traditional commercial users, whilst the improved handling and ride comfort now made the Land Rover attractive to the general public.