The Fiat-Ansaldo L 6/40 light tank was developed as a necessary successor to the CV 33/L 3 tankette series, whose limitations had become increasingly apparent during the interwar period. Initial development began as a private initiative by Ansaldo in 1935, aiming to produce a vehicle for the export market. Between 1935 and 1940, more than a dozen different configurations were tested, ranging from modified L 3 hulls with turrets to designs featuring 37mm guns mounted in the casemate. The final design was officially accepted by the Italian Army in March 1940, receiving the designation L 6/40 based on its weight of approximately six metric tons and its year of adoption.

The technical structure of the L 6/40 featured a hull constructed of riveted steel plates over the fighting and engine compartments. Its armor protection consisted of 30mm thick frontal plates, which increased to 40mm on the gun mantlet, while the sides and rear were protected by 14.5mm to 15mm of steel. The vehicle utilized a torsion-bar suspension system with two double-wheel bogies per side and was powered by a 68 to 70 HP SPA 18 VT four-cylinder gasoline engine. This powerplant allowed for a maximum road speed of 42 km/h and an operational range of approximately 200 kilometers.

Armament for the production model consisted of a 20mm Breda Model 35 quick-firing cannon and a coaxial 8mm Breda Model 38 machine gun, both mounted in a 360-degree rotating turret. The ammunition load typically included 296 to 312 rounds for the 20mm cannon and 1,560 rounds for the machine gun. The tank was operated by a crew of two: a driver seated in the right front of the hull and a commander-gunner who occupied the turret. This two-man arrangement was often criticized, as it overburdened the commander with the tasks of observing, commanding, and manning the weapons simultaneously.

Production of the L 6/40 was marred by industrial delays and shifting military priorities. An initial order for 583 units placed in March 1940 was later reduced to 283 tanks, with the remaining chassis diverted to the production of the Semovente L 40 da 47/32 self-propelled gun. Ultimately, historical records suggest that between 402 and 444 light tanks were completed.

The L 6/40 saw its combat debut in North Africa in late 1941 and was subsequently deployed to several theaters, including the Eastern Front, the Balkans, France, and Sicily. It was primarily issued to armored reconnaissance groups (R.E.Co) and Bersaglieri units, replacing older L 3 tankettes in the reconnaissance role. However, its combat performance was generally considered unsatisfactory. The vehicle suffered from stability issues due to its high center of gravity, and its cross-country mobility was inferior to the AB 40/41 armored cars, with the narrow tracks frequently sinking in soft ground. On the Eastern Front, the L 6/40 represented the heaviest Italian armor deployed, but the units suffered significant losses during the 1942 retreat due to mechanical failures, lack of fuel, and the harsh winter climate.

Several variants were derived from the L 6 chassis, most notably the Semovente da 47/32 assault gun. Other versions included specialized command vehicles (Carro Centro Radio) equipped with additional RF 1 CA and RF 2 CA radio sets, and a specialized ammunition carrier designed to supply the Semovente da 90/53 with 90mm rounds. Prototypes for a flamethrower variant and a caterpillar tractor known as the Cingoletta were also developed but did not enter mass production. Following the Italian armistice in September 1943, approximately 106 L 6/40 tanks were seized by German forces, who designated them as Panzerkampfwagen L6/40 733 (i) for use in anti-partisan duties in Italy and the Balkans. A small number of surviving vehicles continued to serve with the Italian Public Security Police until approximately 1952.