In 1934, the French Army issued a new requirement for a cavalry tank in an attempt to modernized its inventory amidst growing regional unrest. At this time in history, several armies - including that of the British and Soviet - were allied to the doctrine of armored warfare that called for "fast tanks" to exploit weaknesses along a defensive front and cause general havoc at the rear coupled with slower-moving, better protected "cavalry tanks" that could work in conjunction with infantry in smashing enemy positions outright. The British knew their fast tanks as "cruiser tanks" and their cavalry tanks as "infantry tanks". As such, the French requirement was consistent with this doctrine and this produced what was, more or less, a medium-class tank development when compared to contemporaries of the time. A prototype developed by the French SOMUA concern (the Schneider subsidiary out of St. Ouen , otherwise known as Societe d'Outillage Mecanique et d'Usinage d'Artillerie - "SOMUA") was selected for adoption in 1935 with an initial order some 50 units. Production began soon after and orders increased to 600 examples before falling to a more manageable 250 due to financial restrictions. In French Army service the vehicle was designated as the "Automitrailleuse de Combat (AMC) Modele 1935S" but became known to the world simply as the "S35". Initial production versions were delivered in January of 1936.
The tank was designed around the prospect of a defensive-minded war where its primary enemies would either originate from Germany or the Soviet Union to which these armies would field the Panzer III Medium Tank and BT Fast Tank respectively. As such, priority was given to capable armament and armor within a truly modern structure. The French tank was well-armed with a 47mm SA 35 series main gun, one of the most powerful fitted to any time of the decade. Its powerplant of 1 x SOMUA V8 gasoline-fueled liquid-cooled engine delivered 190 horsepower provided for a top road speed of 25 miles per hour with a range out to 143 miles. Both were excellent qualities and would serve the S35 chassis well, the engine fitted conventionally to a rear-set compartment. Suspension was via leaf-spring bogies with nine small road wheels to a track side. The drive sprocket was mounted at the rear of the track system whilst the track idler was set to the front of the hull. The S35 was, therefore, gifted with a powerful engine of good reserves with a voluminous internal fuel store. Fuel stores were self-sealing for increased crew survivability. The 47mm main gun was supplemented by an optional anti-infantry 7.5mm Mitrailleuse mle 1931 machine gun fitted in a coaxial mount in the turret. The one-man APX-1 series turret itself was taken from the Char B1 Heavy Tank. Casting was used for the hull and turret, the hull being made out of two major halves and joined along a line by bolts. The use of casting was rather notable during a time when many nations continued support of weaker riveted tank armor. Casting also allowed ballistic-retarding shapes to be formed thusly improving protection for the crew and systems alike. While each S35 system was to feature the ER28 radio set, these were not available in the numbers required and were thusly afforded only to special command tanks at the platoon level (five S35 systems per platoon). The S35 was crewed by three personnel made up of the commander, driver and radio operator - the commander in the turret and the driver at the front-left hull, the radio operator to his right. All told, the vehicle weighed in at just over 19 tons. Armor protection was excellent with 47mm noted across the hull and 40mm at the turret and minimum armor was 20mm along certain facings. The armor was sloped or curved in various areas. The main gun was afforded 118 x 47mm projectiles while 1,250 rounds of 7.5mm machine gun ammunition were carried aboard.
The SOMUA S35 design was a fast and powerful tank for its time - considered by many to be the best medium tank of the 1930s and the best combat tank on the battlefields of 1940. It certainly was the finest French Army tank of the war. At the time of the German invasion of France in May of 1940, there were 418 S35 tanks produced though only some 250 were actually made available to frontline forces charged with stemming the German assault. Among these few in play, the S35 performed admirably well against a determined foe. Production lasted until the Fall of France in June of 1940.
The SOMUA S35 proved an acceptable type to even the conquering Germans who made a habit of reconstituting captured enemy stocks for localized defense, security and training. The S35 fell into this role for as many as 297 were reused by the German Army under the designation of PzKpfW 35-S 739(f), the "f" indicating their French origin. The Germans also saw fit to add a much-needed cupola to the S35 turret which benefitted the commander. Among these stocks, the German Army passed 32 examples on to the Italian Army to beef up Italian armored divisions which relied largely on outmoded light-class tanks in 1941. Similarly, Bulgaria took delivery of six examples in 1943. Hungary accepted two units earlier in 1942.
However, as strong as the S35 design was, there were many-a-wrinkle that dampened its battlefield reach. One key limitation was in the use of a one-man turret. This forced the commander - residing in the turret - to manage his commanding duties, loading and firing of the main gun and machine gun while receiving and reacting to messages from the radio operator all the while keeping a watchful eye on the unfolding tactical situation around his vehicle and of that near his platoon as a whole. As such, full efficiency of S35 units were ever rarely reached in the heat of battle. The profile of the S35 was also rather tall which made it a most tempting target to anti-tank crews or enemy tank gunners. While the use of casting in the hull's construction was innovative, the decision to manufacture these as two major halves joined by a ring of bolts ensured that the hull would split at the seams after a specially-placed direct hit. The shortage of radios limited the tactical scope of an S35 platoon and French armored doctrine of the time concentrated armored forces into small reactionary groups along a scattered front which led to unfavorable results for French forces during the Battle of France. The S35 was also a complicated and expensive beast to manufacture meaning that only a few could be produced in a given amount of time. To add insult to injury, labor strife at home ultimately limited production of S35 tanks in the short-term. The complexity of the suspension system proved unreliable in the long run and required high levels of maintenance which were unacceptable for a fighting machine. Add to all this the general inexperience of French tanker crews and leaders and one begins to understand the inherent limitations in the French defense.
In practice, the S35 outclassed the German Panzer III offering in armor, firepower and mobility. The German design bested the S35 in tactics and overall powertrain reliability which proved greater than the qualities of the French system. Despite this, the S35 formed a very real threat to German expansion into French territory and were justly dealt with through concerted armor drives and direct dive-bombing attacks when possible. Internal issues and the advent of German Blitzkrieg tactics ultimately limited production and delivery to frontline forces and restricted the legacy of what was a very fine tank of the 1930s. Only 430 of the type were produced in all. There proved a late attempt to fit a 220 horsepower engine into the S35 series as well as improved various facets of the design as the "SOMUA S40" though this yielded no suitable production numbers. Another initiative produced the 75mm-armed S35 (as the SAu 40) self-propelled gun in prototype form which would have been helpful in the defense of France but the German invasion put an end to these promising developments and any intended subsequent production. There were 72 SAu 40 SPGs slated for production. A 1945 initiative intended to fit the excellent British 17-pdr (76.2mm) anti-tank gun to the S35 but this fell to naught.
In 1944, when the Allies pushed their way through France, S35 tanks that were recovered intact were delivered to awaiting Free French forces who continued their use against pockets of German resistance. While still a relatively effective fighting machine to a certain extent, the S35 was eventually outclassed by better armed and armored combat tanks appearing in greater numbers. The American M4 Sherman proliferated the inventories of the Allies to a high degree and many capable variants arose to counter German advances. The 47mm main gun of the S35 was eventually limited by 1944 standards but could still serve a purpose against lesser armor or dug-in foes. Even the German Army listed a dozen functional S35 tanks in December of 1944. There was some noted Japanese interest in the captured S35 production lines leading up to 1942. However, no production examples were ever delivered to the Empire of Japan for use in the Pacific Theater.