The army version was officially known as "Truck, 1/4 ton, CT, 4×4, Cargo & FFW, Austin Mk.1" however the civilian name "Champ" was universally, if unofficially, applied to it.

Testing revealed serious shortcomings and the design was improved by a team at the government Fighting Vehicles Research and Development Establishment (FVRDE) under the leadership of Charles William "Rex" Sewell.

Approximately half of the contract were to be basic vehicles known as Cargo trucks and the remainder were to be fitted with high-output generators and additional batteries in order to power radio equipment.

This version, designated model WN3, was mostly fitted with a modified Austin A90 Atlantic 4-cylinder engine as a cheaper option than the more complex B40 but the vehicle attracted few customers and only about 500 were built, the great majority of these being exported.

A few were fitted with additional equipment for use as field ambulances, telephone line-laying vehicles or equipped with armour and a .303 in Vickers medium machine gun or .303 Bren light machine gun utilising the built-in pintle mount forward of the windscreen, but the majority served as cargo/personnel carriers or were fitted with radios.

As the Champ entered service it became apparent that although it had an outstanding cross-country performance, it was too expensive (£1200 at 1951 prices), too complex and had limited use outside of the narrow field combat role for which it had been designed.

The Champ served with the British Army in the UK, Africa, Germany, Cyprus, Libya and the Suez Campaign, and early vehicles were sent for troop trials at the end of the Korean War.

These mass sales made them cheap to buy (£150 being typical in 1966) and with fuel at low 1960s prices, many were bought as "fun" vehicles and used with little regard to the routine maintenance that the complex design required.

With the adoption in 1949 of Unified thread standards, the engine was re-designed and simplified to ease manufacture; a cast-iron cylinder head was used in this version which can be most easily identified by the letters "UNF" cast or pressed into the rocker cover.

A conventional Borg & Beck clutch with mechanical linkage was used and drive from the gearbox was by shaft to the rear combined transfer box and differential assembly which incorporated reverse gear, thereby allowing five reverse gears also, and then by a long shaft to the front differential which incorporated a simple dog clutch to enable four-wheel drive when required.

Each wheel station was also fitted with a rubber cone and cup system to buffer extreme upward suspension travel with energy control exercised by double-acting telescopic hydraulic dampers.

The braking system was supplied by Girling and employed drums and a simple single-line hydraulic layout without power assistance.

The body was a utilitarian open four-seater tub of welded pressed steel panels, supplied by the Pressed Steel Company, and similar in style to the war-time Jeep layout although unlike the Jeep, the Champ body is designed to carry part of the vehicle stresses and chassis flexing.

A 20-gallon (91 litre) fuel tank was located at the rear of the vehicle, giving an operational range of approximately 300 miles.

Commercial 12-volt electrical components by Lucas Industries were provided and facilities for power take-off, driven from the transfer box, were available.