The Fiat-Ansaldo M11/39 was an Italian medium tank used from 1939 through the early period of World War II. Although designated a medium tank by the Italian Army, in weight and firepower it was closer to contemporary light tanks. The designation M11/39 is understood as follows: "M" for Medio (Italian: "medium"), followed by the weight in tons (11) and the year of adoption (1939).
The M11/39's career was cut short due to several weaknesses of its design. The most important was the placement of the main 37 mm armament in the hull. The 37 mm gun was in a fixed position with traverse restricted to 15° to port or starboard. The only other armament was the dual 8 mm machine guns in a rotating turret. While the machine guns were served by only one man, the turret was cramped and manually operated.
The concept was to use the main gun against heavy targets and defend the tank against all-round threats with the turret armament. The layout was similar to the American Grant/Lee tanks, still to come in 1939. The original intent was to place the 37/40 mm armament in the turret, but there was insufficient space. A redesign of the M11/39, in order to mount the main gun in the turret, was commenced, finally resulting in the development of the M13/40. In the meantime an order for 100 M11s was placed.
In addition to the poor gun positioning, the M11/39 had other shortcomings: its endurance and performance were both poor, it was relatively slow, its mechanical reliability was very poor, and its 30 mm maximum riveted steel armour, designed to withstand only 20 mm fire, was vulnerable to British 2-pounder guns at any range at which the M11/39s main gun was useful.
All M11/39s were designed to carry a radio, but none of the production vehicles were so fitted. The M11/39 hull design, with modifications, was used in the development of the more successful Fiat M13/40.
The M11/39 proved somewhat successful in early encounters with British light tanks like the Mk VI. The 37 mm gun of the M11 acted as a deterrent against attacks by these relatively fast but thin-skinned vehicles armed only with machine-guns. However, the M11/39 was outclassed by heavier British cruiser and infantry tanks such as the A9, A10, A13, and Matilda.
From 10 April 1941, during the siege of Tobruk, a few captured M11s were employed by the 6th Australian Division Cavalry Regiment over some months. They painted large white kangaroo symbols on the tanks to clearly identify them. The Australians used the captured M11s, together with several M13s, until they ran out of diesel fuel. The tanks were then destroyed to prevent re-use by advancing Axis forces in the spring of 1941.