The Italian Army did little to keep their artillery inventory modernized after World War 1 (1914-1918). By the time of World War 2 (1939-1945), there proved few solutions on the horizon and the Army eventually went to war with many aged pieces of varying effectiveness. It was not until the late 1930s that the Army finally moved on upgrading its artillery stock and adopted two towed pieces for separate battlefield roles - a direct-fire field gun and an indirect-fire howitzer. The latter became the "Obice da 210/22 Modello 35" (also "Model 1935", "M1935" or "M35").
Design of the howitzer was undertaken by a group from the Servizio Tecnici Armi e Munizioni (STAM) of the Italian Army. A prototype was made available in 1935 though the weapon was not formally taken into inventory until 1938 with its designation still showing its 1935 roots. The initial Italian Army order was for 346 units to replace outgoing types and serial manufacture was handled by Ansaldo of Pozzuoili.
The all-modern Model 35 system ended up becoming an excellent artillery piece of the period. Its listed caliber was 210mm (8.3") and its weight was 35,020 pounds when arranged to fire and 53,000 pounds when broken down to travel. Transport was aided through the unit being reduced to two major components for hauling and these could be further broken down to four smaller components for longer transport. The howitzer fired a 223 pound shell out to 16,800 yards at a velocity of 1,800 feet per second. The gun's mounting hardware allowed for 0 to +70 degree elevation spans and inherent 75-degree traversal. The split trail carriage was used as both the transport carriage and gun support and included four road wheels (two per side) in its design. The wheels were raised from the ground prior to firing with a base lowered to support the weapon (at about the rear axle). The split trail arms were spread out and dug into earth via spikes to help counter recoil. With the wheels raised and the support base lowered, the gun was able to traverse a full 360-degrees which was a tactical advantage. A recoil mechanism (hydropneumatic) was also integrated into the barrel's function. The barrel measured 16.4 feet long.
Despite the extremely promising nature of the Model 35 gun, Italian industry was not up to the task of mass producing the product. By the time of the Italian entry into the war, few guns were on hand so reliance fell once again to the aged stocks already in circulation with the Army. By the fall of 1942, only twenty of the guns were in the Italian inventory from the initial 24 units sought from 1938 with production helped by OTO participation. A second order in 1939 called for 66 more guns but this was reduced in 1941 to 46 units and, then again, in 1943 for 34 guns.
The German invasion of the Soviet Union only worsened Model 35 availability. The Italians had entered into an agreement with another Axis player - Hungary - to supply the new gun in exchange for resources and other war goods. As such, the guns were shipped from Ansaldo lines directly to Hungarian ownership as they were completed. Once in Hungarian Army service, they took on the designations of 21cm 39M, 40M, and 40Ma (also "40a.M") and were fielded against Soviet forces along the East Front. Differences between the models were slight with the 39M being original models from Italy in 1940, the 40M introducing some Hungarian-inspired modifications to the carriage, and 40Ma being the last batch production model appearing during 1943. Some local manufacture within Hungary of the guns eased modifications and delivery to the Army.
The gun proved effective enough that it was commandeered by the Germans upon the surrender of the Italians to the Allies in September of 1943. Even the OTO production lines were ordered by German overseers to keep up manufacture for the Wehrmacht and the guns were used with great efficiency as defensive set pieces against the advancing Allies. In the German Army inventory, the guns were handed the designation of "21cm Haubitze 520(i)" with little in their design having been changed. These guns fought on - and were produced - until the end of the war in Europe in May of 1945.
With the conclusion of hostilities in Europe and the dust beginning to settle, Ansaldo attempted to interest several foreign parties in its field piece. However, with the glut of American war goods readily available to virtually any taker, there proved little-to-no market for the howitzer which eventually led to it falling away to history. It saw no more operators than what was seen in wartime.
Italian Army use of the gun continued in the decades following the war. All Obice da 210/22 Modello 35 guns were out of service by 1969, replaced by the American M115 (as the "Obice da 203/25").