While the 37mm PaK 35/36 anti-tank cannon proved a success during its trial in the Spanish Civil War, German authorities knew that the system would quickly become outmoded by heavier armored tank systems (some already in service at the time). Rheinmetall of Germany began work on a towed 50mm (2-inch; 5-cm) caliber version in 1935 with the designation of PaK 37. However, German authorities were not satisfied with the weapon's low-velocity action, forcing Rheinmetall to rework their product. The company fitted a new, longer L/60 barrel and returned with the PaK 38 to which the Germany Army accepted for production. Production began in 1939 and examples reached German troops in 1940, though this was too late to take part in the German campaigns across the West Front. Once in service, the PaK 38 operated as part of dedicated anti-tank platoons though it would not be until 1941 that the anti-tank gun would not see its first combat actions - this as part of the German invasion of the Soviet Union through "Operation Barbarossa".
By the time of the German assault into Soviet territories, PaK 38 teams were handed a new projectile - the Panzergranate 40 APCR (or "AP40"). The ammunition was based on captured Czech and Polish ammunition designs reinstituted back into service with the German Army. The AP40 utilized a dense tungsten core, providing for better penetration capabilities at distance and proved particularly effective against the Soviet KV-1 heavy tank. At the time of the T-34/76 medium tanks arrival on the East Front, the PaK 38 and its AP40 round proved the only weapon then in service capable of penetrating its thick armor. However, the PaK 38 was only available in limited numbers and this severely limited her reach on the front, forcing the Germans to bring up old captured French 75mm guns to fill the gaps in their defense. While the T-34/76, in some ways, made the excellent 50mm PaK 38 something of a liability now, the weapon system would still go on to serve through to the end of the war in 1945 - even despite having been replaced by newer, larger-caliber anti-tank guns.
The PaK 38 fielded a maximum range of nearly 3,000 yards. Caliber was of 50x419mm R and the weapon exhibited a length of 10 feet, 5.5 inches with a 7 feet, 9.7 inch barrel. The barrel sported a baffled muzzle brake to help dispel recoil while the towing carriage served double duty by providing the "legs" to stabilize the weapon when set to fire. The weapon system as a whole weighed 2,341lbs when linked up for travel and displaced 1,000lbs when set down in place. Traverse was limited to 65-degress with an elevation of -8 degrees to +27 degrees. Depending on the ammunition used, muzzle velocity could be rated at as high as 3,870 feet per second for AP (armor piercing) rounds and as low as 1,805 feet per second for HE (high-explosive) rounds. The weapon operated from a semi-automatic action while the feed system was manually operated by the crew, allowing for rates-of-fire around 13 rounds per minute. Sights were Z.F. 3x8.
The crew of five clustered around the rear of the weapon system, protected only by the forward-facing sloped, curving armor plate. The plate was set as two individual components fitted roughly 1 inch apart and were 0.15 inches in thickness. This supplied the crew with forward facing protection but further safety would have to come from the nearby environment in the form of earthen structures, tree coverage, man-made fortifications such as sandbag walls and the like. Steel rubber-tired wheels allowed the PaK 38 to be towed by vehicles at speed. The ends of the trail leg spades featured dolly wheels for additional maneuvering support - though these were often removed. Once in place, the weapon was set in position with its tubular, light alloy split-trail carriage. When opened, the legs locked the torsion bar suspension of the carriage in place for firing. The weight of the PaK 38 ensured that it could be towed into action by a tractor, halftrack or utility truck and that the crew could work together in relocating the artillery piece to a new nearby position. The PaK 38 presented enemies with a rather small, low-profile frontal target thanks to its well thought-out design.
The PaK 38 proved such a success throughout its tenure that the weapon was designed for use aboard combat aircraft. This particular development introduced an automatic feed mechanism and was showcased in one proposed development of the jet-powered Messerschmitt Me 262 "Schwalbe". The weapon was intended as a heavy gun suitable in downing enemy bombers that were consistently wreaking havoc on German infrastructure and war production facilities. Another proposed development was using this same aircraft-base automatic cannon as a ground-based anti-aircraft gun system. The PaK 38 was also developed into a vehicle main gun armament for use in tanks and many of these eventually ended up as shoreline fortifications along the "Atlantic Wall". In yet another battlefield use, the PaK 38 was fitted atop the rear of tracked Panzerjager carriages to produce a make-shift self-propelled gun (SPG) system to support of infantry actions. So many of these systems were produced, in fact, that the British ultimately captured enough examples to place them into their own ranks as an emergency measure should they be needed.
Some 9,500 PaK 38 systems were ultimately produced before the end of the war and a great quantity were still in use up to the end.