The 3.7-cm PaK 35/36 ("PaK" for "PanzerAbwehrKanone") was the standard-issue anti-tank cannon of the Wehrmacht by the time of the German invasions of 1939. Like other German systems in development during the 1930's the PaK 35/36 was field tested in the Spanish Civil War and with good results. The PaK 35/36 proved the importance of portable crew-served anti-tank weapon systems, particularly in these early campaigns. But by 1940, progressively thicker armor had begun appearing on British, French and Russian enemy tanks, forcing the light-caliber PaK 35/36 system to quickly fall out of favor as a frontline tank killer. Development by the Rheinmetall company of this dedicated anti-tank cannon for the German Army began as early as 1925. 14,459 PaK 35/36 systems were reportedly delivered with production beginning in 1928.
The PaK 35/36 was a light battlefield weapon relatively easily maneuvered into position by its crew and towed to hotspots via pack animal or vehicle. Its relatively small size also allowed for concealment by her crews, an advantage when ambushing unsuspecting enemy vehicles. The main force behind the PaK 35/36 was its potent 37mm L/45 barrel nestled within an angled armored shield straddled on either side by two road wheels and anchored by two split-trail tubular legs. Wheels were initially of the spoked wheel-type for improved horse traction as the German Army was still relying heavily on pack animal-towed artillery at this point in history but these eventually gave way to steel wheels with pneumatic tires in 1934, now making the PaK 35/36 system suitable for towing via vehicle. The crew of three remained relatively exposed - save for the shield and any other natural protection - when loading and firing the weapon.
Ammunition types ran the gamut of armor piercing, high velocity, high explosive and hollow charge type projectiles. Elevation was limited to -5 t +25 with a traverse of 60 degrees. Muzzle velocity was a reported 2,500 feet for armor piercing rounds and 3,400 feet for HVAP and APCR projectiles. The effective range was about 2,000 feet (other sources report a much lower effective range).
On the West Front, the PaK 35/36 excelled against the lightly armored vehicles found in the Spanish Civil War and proved equally potent against the Polish defense forces years later. The weapons reach would soon hit its ceiling when facing off with the British Matilda II and French Char B1 heavy tanks - PaK 35/36 projectiles ricocheting off the thick armor of these steel beasts. On the East Front, the PaK 35/36 was still in frontline service in 1940 despite its official replacement by the 5cm PaK 38 towed artillery series. It did, however, still prove effective against the Russian BT-7 and T-26 series of light tanks but the arrival of the stout T-34 medium series (and even the lumbering heavy KV-1 and KV-2 models) rendered the PaK 35/36's usefulness wholly obsolete. Its ineffectiveness by this point had garnered the PaK 35/36 the adequate nickname of "Heeresanklopfgerat", translating to "army door-knocker".
Attempts were made to shore up the ineffectiveness of the PaK system by introducing a new projectile type into the mix - the armor-piercing "Panzergranate 40" featuring a wolfram core. Unfortunately in practice, the new round failed to provide the added punch and so an even newer projectile was devised - the "Stielgranate 41" - this with a hollow charge and stabilizing tail plane. Fielded in 1942 with the PaK 35/36 and its new projectile was of some benefit though the low muzzle velocity of the PaK 35/36 barrel itself meant that the crew needed to be some distance closer to the enemy tank target than was deemed comfortable.
As a whole, production of the PaK 35/36 was stopped from 1942 onwards though - by sheer surplus - the weapon was fielded in quantity while other larger caliber weapons were being designed and put into production alongside her. The PaK 35/36 did prove useful in an auxiliary role, specifically when mounted on mobile platforms such as the SdKfz 250 and SdKfz 251 half-tracks (when fielded in the light anti-armor support role). Thanks to the weapon system's portability, Fallschirmjager ("parachute") units were also issued this anti-tank cannon along with garrison and training units. At any rate, the PaK 35/36 secured its legacy by introducing many-a-nation to a proven anti-tank weapon from which to design their own successful versions from.