In March 1943, the last wartime variant of the Marmon-Herrington series was introduced. It was completely redesigned and rapidly entered production. A real improvement over previous designs, it introduced a larger turret armed with a two-pounder gun (40 mm/1.575 in). This put its firepower on par with most British early war designs, and was more than adequate to face enemy reconnaissance vehicles. This was also the version with the most prolonged active service, soldiering until the 1980s in many countries. A testimony to its reliability, ruggedness of design and construction.
The Mark IV had a monocoque steel hull, 12 mm (0.47 in) thick at the front and 6 mm (0.24 in) elsewhere. The engine was rear mounted and the turret sported a 2-pounder gun (40 mm/1.575 in), with a coaxial 0.3 in (7.62 mm) Browning machine gun. The driver was located in the narrow front compartment, and had a bulletproof window, protected by a large armoured shutter with a single sight slit. The sides also had similar large windows with shutters. This provided the driver with excellent peripheral vision. Both the front and the rear sections were much narrower than the centre. Tooling straps were installed on the right-side slope. Two sand ramps were attached to the chassis and formed an open storage.