The main difference in the M20 lay in the absence of the 37mm gun turret, which was replaced by an open-topped compartment fitted with a Browning M2 heavy machine gun of .50 calibre (12.7mm), offering a degree of defence against infantry and aircraft. To compensate for the lack of anti-tank weaponry, the crew was also issued with a bazooka.
The aim of the new variant was to create a lighter, faster, and more versatile vehicle for reconnaissance, liaison, and command duties, capable of operating with agility at the front lines. Its relative lightness and mobility made it ideal for accompanying motorised columns and providing support to armoured and mechanised cavalry units, often fulfilling similar roles to the M3 half-track.
The relatively thin 19mm armour provided some protection against shrapnel and small arms fire, but a major vulnerability remained: the base plate was just 6mm thick, offering little protection against landmines. As a result, some crews opted to place sandbags on the compartment floor to enhance survivability.
Conversely, the open top of the compartment allowed for excellent visibility and easy access, albeit with less protection for the crew compared to the enclosed M8 version. A noteworthy detail was the standard inclusion of a radio communication system, which enabled the M20 to function as a mobile command post when required.
With a crew of between two and four, the M20 could reach speeds of around 90 km/h and had a range of over 500 km, thanks to the relative efficiency of its six-cylinder Hercules JXD petrol engine. Moreover, the JXD ran more quietly than other engines of similar output used in comparable American military vehicles – a much-appreciated trait that contributed to the M20’s relative stealth in combat, reducing the chance of detection by enemy forces and allowing for an element of surprise unavailable to other vehicles of its class. For this reason, the M8 and M20 armoured cars of Patton’s Third Army became known as “Patton’s Ghosts”.
A total of 3,680 M20s were built by Ford during the two years of production, with the vehicle deployed mainly in the European theatre, but also in Asia and later during the Korean War. Withdrawn from U.S. Army service shortly after the 1953 Armistice, many M20s were rebuilt and redistributed among various allied nations, where they remained in service into the 1960s.
As a textbook example of American military doctrine focused on mobility and flexibility, some units also saw post-war use in police or patrol roles in conflict zones, including in the Allied occupation areas.