A British Army specification for a light truck was issued in the late 1940s, inspired by the Jeep but able to perform in all theatres of operation of the British Army. It was considered important that a British-made vehicle was produced in order to reduce the reliance on US vehicles and the foreign expenditure that entailed.
A project to design a "Car 4×4 5 cwt FV1800-Series" was launched in 1947, and the Nuffield Organisation built three prototype designs known as the "Nuffield Gutty". 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. The suspension system was designed by Alec Issigonis, who went on to design the Morris Minor and the Mini.
About 30 prototypes of the improved vehicle were built by Wolseley Motors Limited under the name "Wolseley Mudlark", and after further refinement the design was formalised as FV1801(a). The Austin Motor Company was awarded the contract to produce 15,000 vehicles and a former aircraft factory at Cofton Hackett, on the edge of Austin's Longbridge complex in Birmingham, was fitted out for the work.
The engine was a four-cylinder in-line petrol unit of 2838 cc capacity (3.5-inch-diameter (89 mm) pistons × 4.5-inch (110 mm) stroke) designed by Rolls Royce and was the smallest of the standardised B-Range military engines. These engines had their origin in a 1936 design produced at Derby, with the concept and dimensions first developed for the Rolls-Royce 20 HP of 1922, but with the demands of the war, development was not proceeded with until the late 1940s. The engine was designed with absolute reliability as a prime criterion with fuel economy a secondary consideration, and using British Standard Fine (BSF) thread standards. A feature of this engine was the use of a cast aluminium cylinder head with screwed-in hardened steel valve seats.