Something of an anachronism in the 2000s, the Defender has no unibody structure and is still largely hand assembled. All its major body panels and sub-assemblies simply bolt together. Thus not only can a Defender be literally broken down to its chassis with simple hand tools there are no irreplaceable stress points. While appreciated in the field and by enthusiasts, this method of manufacture has become increasingly expensive relative to unibody and modular construction.
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 93 inch (2.362 m) wheelbase, and Land Rover 127, with 127 inch (3.226 m) 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. While the engine and other body panels carried over from the Series III, mechanically the Ninety and One Ten showed significant modernisation, including:
In addition, a new series of progressively more powerful and more modern engines were designed for future use.
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, 68 hp (51 kW) 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 in conjunction with a 5 speed transmission 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 spring 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.
The original One Ten of 1983 was available with the same engine line-up as the Series III vehicles it replaced, namely 2.25 litre petrol and diesel engines, and a 3.5 litre V8 petrol unit. The intention had always been to provide more powerful engines as soon as the new vehicles had found their feet and the Series III had ceased production. Indeed, in 1981 the 2.25 litre engines had been upgraded from 3- to 5-crankshaft bearings in preparation for the planned increases in capacity and power.
The 2.5 litre version of the diesel engine, producing 68 hp (51 kW), was introduced in both the One Ten and the newly-arrived Ninety. This was a long-stroke version of the venerable 2.25 litre unit (the new version displaced 2495 cc), fitted with updated fuel injection equipment and a revised cylinder head for quieter, smoother and more efficient running. A timing belt also replaced the older engine's chain.
In 1985 the petrol units were upgraded. An enlarged 4-cylinder engine was introduced. This 83 hp (62 kW) engine shared the same block and cooling system (as well as other ancillary components) as the diesel unit. Unlike the diesel engine, this new 2.5 litre petrol engine retained the chain-driven camshaft of its 2.25 litre predecessor. At the same time, the 114 hp (85 kW) V8 was also made available in the Ninety- the first time a production short-wheelbase Land Rover had been given V8 power. The V8 on both models was now mated to an all-new 5-speed manual gearbox.
1986 saw an important development. For many years Land Rovers had been criticised for their low-powered engines, which, despite the recent improvements, still lagged a long way behind much of the competition. Designed to be simple and durable, the engine had worked for decades, but the venerable engines began to feel old-fashioned and underpowered in an era of high horsepower motors. Drivers were less inclined to use the gearbox to compensate for the older motor's relative lack of power. The "Diesel Turbo" engine was introduced to make up for this long-standing shortfall. The engine was essentially a lightly-turbocharged version of the existing 2.5 litre diesel, with several changes to suit the higher power output, including a re-designed crankshaft, teflon-coated pistons and nimonic steel exhaust valves to cope with the higher internal temperatures.  Similarly, an 8-blade cooling fan was fitted, together with an oil cooler. The 2.5 diesel, 2.5 petrol and Diesel Turbo engines all shared the same block castings and other components such as valvegear and cooling system parts, allowing them to be built on the same production line. The Diesel Turbo produced 85 hp (63 kW), a 13% increase over the naturally-aspirated unit, and a 31.5% increase in torque to 150 lb·ft (203 N·m) at 1800 rpm. This finally provided a powerful yet economical powerplant for the vehicle. Externally, turbodiesel vehicles differed from other models only by having an air intake grille in the left-hand wing to supply cool air to the turbo. The engine was only intended to be a short term solution to compete with more advanced Japanese competitors, but was quickly adopted as the standard engine for UK and European markets.
Early turbodiesel engines gained a reputation for poor reliability, with major failures to the bottom-end and cracked pistons. A revised block and improved big end bearings were introduced in 1988, and a re-designed breather system in 1989. These largely solved the engine's problems, but it remains (like many early turbodiesels) prone to failure if maintenance is neglected. Well-maintained engines are capable of long service lives in excess of 150,000 miles (240,000 km). Despite its early problems, the Diesel Turbo was a popular engine choice in its time, especially since it offered improved power, torque and economy over the 2.5 litre petrol engine. Contemporary road-testers compared the engine favourably to its Japanese competitors, despite the age of the basic design. Whilst not being able to match the performance of a V8-engined Land Rover, the Diesel Turbo provided adequate performance for most commercial and private buyers and was a key aspect in Land Rover's sales revival (see below).
The biggest change to the Land Rover came in late 1990, when it became the Land Rover Defender, instead of the Land Rover Ninety or One Ten. This was because in 1989 the company had introduced the Discovery model, requiring the original Land Rover to acquire a name. The Discovery also had a new turbodiesel engine. This was also loosely based on the existing 2.5 litre turbo unit, and was built on the same production line, but had a modern alloy cylinder head, improved turbocharging, intercooling and direct injection. It retained the block, crankshaft, main bearings, cambelt system and other ancillaries as the Diesel Turbo. The breather system included an oil separator filter to remove oil from the air in the system, thus finally solving the Diesel Turbo's main weakness of re-breathing its own sump oil. The 200Tdi as the new engine was called produced 111 hp (83 kW) and 195 lb·ft (264 N·m) of torque, which was nearly a 25% improvement on the engine it replaced (although as installed in the Defender the engine was de-tuned slightly from its original Discovery specification (111 horsepower) due to changes associated with the exhaust).
This engine finally allowed the Defender to cruise comfortably at high speeds, as well as tow heavy loads speedily on hills while still being economical. In theory it only replaced the older Diesel Turbo engine in the range, with the other 4-cylinder engines (and the V8 petrol engine) still being available. However, the Tdi's combination of performance and economy meant that it took the vast majority of sales. Exceptions were the British Army and some commercial operators, who continued to buy vehicles with the 2.5 litre naturally-aspirated diesel engine (in the Army's case, this was because the Tdi was unable to be fitted with a 24 volt generator). Small numbers of V8-engined Defenders were sold to users in countries with low fuel costs or who required as much power as possible (such as in Defenders used as fire engines or ambulances).
Along with the 200Tdi engine, the 127's name was changed to the Land Rover Defender 130. The wheelbase remained the same; the new figure was simply a tidying up exercise. More importantly, 130s were no longer built from "cut-and-shut" 110s, but had dedicated chassis built from scratch.
1994 saw another development of the Tdi engine, the 300Tdi. Although the 200Tdi had been a big step forward, it had been essentially a reworking of the old turbocharged diesel to accept a direct injection system. In contrast the 300Tdi was virtualy new, despite the same capacity, and both the Defender and the Discovery had engines in the same state of tune, 111 bhp (83 kW), 195 ft·lbf (264 N·m).
Throughout the 1990s the vehicle attempted to climb more and more upmarket, while remaining true to its working roots. If ordered without any optional extras, the Defender was a basic working tool. If the owner so wished, any number of options and accessories could transform it into a vehicle that was perfectly acceptable as an everyday method of transport, while still retaining excellent off-road abilities. This was epitomised by limited edition vehicles, such as the SV90 in 1992 with roll-over protection cage, alloy wheels and metallic paint and the 50th Anniversary 90 in 1998 equipped with automatic transmission, air conditioning and Range Rover 4.0 litre V8 engine.
A new variant was the Defender 110 Double Cab, featuring a Station Wagon style seating area, with an open pick up back. Although prototypes had been built in the Series days, it was not until the late 1990s that this popular and adaptable vehicle finally reached production.
In 1993 Land Rover launched the Defender in the North American (i.e. the United States and Canada) market. Although the Range Rover had been sold there since 1987, this was the first time utility Land Rovers had been sold since 1974. To comply with the strict United States Department of Transportation regulations, ranging from crash safety to lighting, as well as the very different requirements of American buyers, the North American Specification (NAS) Defenders were extensively modified. The initial export batch was 525 Defender 110 County Station Wagons. 500 to the United States and 25 to Canada. They were fitted with the 3.9 litre V8 petrol engine and 5-speed manual transmission. All the vehicles were white (except two specifically painted black for Marcos J. Soto and Ralph Lauren). They sported full external roll-cages and larger side-indicator and tail-lights. All were equipped with the factory-fitted air conditioning system.
This initial batch sold quickly, and for the 1994 and 1995 model year Land Rover offered the Defender 90, fitted with a 3.9 litre V8 engine and a manual transmission which was clearly intended to compete with the Jeep Wrangler. Initially, the Defender 90 was only available as a soft-top, but later version was offered with a unique, removable, fibre-glass roof panel or regular Station Wagon hard-top.
In the final year of US production the engine was improved, designated 4.0 and mated to a 4 speed automatic transmission. In 1998 regulations changed to require the fitting of airbags for both front seat passengers in all vehicles, as well as side door impact requirements. The Defender could not be fitted with these without major modifications, which given the small numbers of NAS vehicles sold in relation to Land Rover's global sales, were not economically viable. Land Rover retired its utility vehicles at the end of 1997 to focus on its more upmarket Discovery and Range Rover models, as well as the newly-launched Freelander.