The Vanden Plas designed and built Austin A135 Long Wheelbase 7/8 seater Limousine DM4 was launched at the October 1952 Earls Court Motor Show. Built on a lengthened Austin A135 chassis, the body was built of steel and light alloy panels over a timber frame. It had an 11ft. wheelbase, 17ft 11in. length and 5ft 10in. height. It was powered by Austin's 'D' series in-line 6 cylinder, 3993cc engine with a 4-speed manual transmission and triple SU carburettors. However these were soon replaced by a single Stromberg DVA42 carburettor.
The launch at the 1952 London Show proved a huge success. The first 2 limousines produced were bought by the Royal Household for the new Queen. This order was repeated another three times during the life of the DM4 including the final two vehicles, both of which survive, one at Sandringham and the other at the British Motor Museum, Gaydon.
Like the A135 Princess Saloons DS2 & DS3, the early Limousines carried the Austin Sheerline type radiator grille. However in October 1953 the DM4 received the new 'Vanden Plas' type grille as fitted to the Princess DS3 saloon. The 'Flying A' mascot remained on the grille and the vehicle carried hubcaps with the Austin badge. Trafficators were deleted to be replaced with direction winkers set into the front wings. Automatic transmission became available in 1956.
In 1958 the rather thick rear door pillars were replaced by slim chromium plated pillars to give rear passengers a better view. In 1959 the marque became known simply as 'Princess' and the reference to Austin was removed. The 'Princess' name was added to the centre of the front bumper, the 'Flying A' was removed from the radiator to be replaced by a black coronet badge, and the hubcaps changed to have a central 'P' badge. The rear wheel spats were altered to show more of the rear wheel and rear opening quarter lights were now fitted as standard, being an extra cost option on earlier cars.
In 1960 power steering became available as an option and the marque name changed again and was now known as 'Vanden Plas Princess'. Thus the DM4 became known as the Vanden Plas Princess 4 Litre Limousine, the name it retained until the end of production in May 1968.
The sumptuous interior contained the finest leather, walnut and Wilton carpeting. Vanden Plas used all of their traditional coachbuilding skills to ensure that this elegant vehicle was built to the highest standards.
With the formation of British Motor Holdings in July 1966, a decision was taken to update the DM4. In 1968 Vanden Plas produced a revised DM4 prototype which is shown with its twin headlights and one-piece windscreen. However at the same time Daimler produced the DS420 limousine based upon the Jaguar Mark 10 chassis and mechanics, and this was the car B.M.H. adopted to replace the ageing DM4 and Daimler DR450 Limousines.
The DM4 had always represented good value compared with its rivals.
Some 3238 vehicles were produced in total.