The Carro Armato M 11/39 was developed in the late 1930s as Italy's first modern medium tank, intended to replace the obsolete machine-gun-armed tankettes then providing the bulk of the nation's armored forces. The designation "M" stood for medio (medium), "11" denoted its approximate weight in metric tons, and "39" referred to the year of its official adoption. The project was led by principal designer Giuseppe Rosini at the Ansaldo works, based on specifications issued in 1936 for an infantry support vehicle capable of mountain warfare. Despite initial hopes for a large production run, industrial delays and the development of the superior M 13/40 meant that only 100 units were ever completed between 1939 and 1940.

Technically, the M 11/39 utilized a hull of riveted and bolted steel plates, as the Italian industry was not yet proficient in welding techniques for armored vehicles. Armor protection was relatively thin, ranging from 6mm on the floor to a maximum of 30mm on the frontal plates and the turret. The primary armament was a 37mm Vickers-Terni L/40 gun mounted in a casemate on the right side of the hull, which severely limited its tactical flexibility. This gun was manned by a dedicated gunner and had a restricted horizontal traverse of only 15 degrees to either side. Secondary armament consisted of two 8mm Breda Model 38 machine guns housed in a small, hand-operated turret capable of 360-degree rotation.

The vehicle was powered by an SPA 8T eight-cylinder, liquid-cooled diesel engine that produced between 105 and 125 horsepower. This powerplant allowed for a maximum road speed of approximately 32 to 34 kilometers per hour and an operational road range of roughly 200 to 210 kilometers. The suspension system, derived from an enlarged version of the L 3 tankette design, featured four bogie assemblies on each side, with each pair of wheels supported by semi-elliptical leaf springs. While the suspension itself was considered functional, the underpowered engine and overall mechanical unreliability led to frequent breakdowns during field operations.

Inside the cramped fighting compartment, a crew of three served as the driver, the hull gunner, and the commander—who also functioned as the turret operator. Visibility for the crew was poor when hatches were closed, and high internal temperatures in desert environments often forced crews to operate with hatches open, increasing their vulnerability. Furthermore, the lack of standard radio equipment in production models, with the exception of the prototype, severely hindered coordination between units during combat.

In operational service, the M 11/39 was deployed to North Africa and Italian East Africa. Two battalions saw action during the 1940 offensive into Egypt, but they were quickly outclassed by British armor. By early 1941, nearly all 100 units had been lost in combat, captured, or abandoned due to mechanical failures and a lack of spare parts. Captured vehicles were utilized for a time by Australian forces, who painted large white kangaroo silhouettes on the hulls and turrets to prevent friendly fire. While the M 11/39 was ultimately judged a failure due to its hull-mounted main gun and technical shortcomings, it provided the essential chassis and suspension template for the subsequent M 13/40 and M 14/41 medium tanks.