The 10.5cm K gepanzerte Selbstfahrlafette was a developmental tank destroyer for the German Army in World War 2 that was initially designed around a self-propelled gun requirement. Prior to the German invasion of France, it was always recognized that a portion of German Army success would be attributed to breaking the defenses at the French Maginot Line. The Maginot Line stood as a networked line of concrete bunkers, artillery houses, machine gun nests and vehicle traps with steel obstacles which ran along the French border facing Germany and Italy (this portion known as the "Alpine Line"). This line of defense was intended to slow the progress of an invading force, giving the French national army additional time to mobilize in response. The Line was constructed over a period spanning 1930 to 1940 and was made operational in 1935. While certainly imposing at its core, it was tactically inflexible and, eventually, simply bypassed by the German Army along its flanks.
For the Germans, defeat of these strategic points required a special vehicle under consideration, one that could keep pace with the new mechanized doctrine of the German Army and one with armament capable of defeating the thick concrete houses of the Maginot Line. Work on such a vehicle began in 1938 under the Krupp banner and evolved considerably along the way.
The basic result was an all-tracked vehicle utilizing the chassis of the Panzer IV infantry tank, the Panzer IV developed in concert with the Panzer III which was, itself, intended for direct contact actions against enemy tanks. Between 8,800 and 9,800 Panzer IV tanks were ultimately produced during the course of the war after its adoption in 1939 and she remained the workhorse of German Panzer units until the cessation of hostilities in May of 1945. The drivetrain, chassis, running gear, suspension system and hull would constitute the base foundation of the new German self-propelled gun - designated as "10.5cm K gepanzerte Selbstfahrlafette IVa" (10.5cm K (GpSfl IVa)).
To the existing chassis was added an all-new hull superstructure which incorporated slightly angled armored plates to the front, sides and rear - the top, however, was left open for the headroom required of the gunnery crew. While the Panzer IV made use of the Maybach HL 120 V12 engine of 265 horsepower, it was decided to utilized the smaller, weaker Maybach HL 66 6-cylinder engine of 180 instead. This powerplant was mated to a Zahnradfabrik SSG 46 series transmission system. The suspension system remained of the leaf spring type. Maximum road speed was 17 miles per hour with an operational range of 105 miles.
Key to the vehicle's success was the selection of the 105mm (10.5cm) K18 L/52 gun which was based on the 105mm schwere Kanone 18 field gun introduced in 1934. This system used two-piece ammunition which meant that projectiles and propellant charges were managed separately, the projectile entered into the gun breech followed by the powder charge. The barrel was capped by a massive double-baffled muzzle brake and a thick mantlet was seated at the entry point into the superstructure's frontal face. 26 x 105mm projectiles would be carried aboard.
Outwardly, the vehicle was a stout and imposing design. The Panzer IV roots betrayed her as her track system remained unchanged from the original's. There were eight small double-tired, rubber-lined road wheels to a track side with the drive sprocket at front and the track idler at rear. Four track return rollers guided the upper track portions about. No side armor skirts were afforded. The hull superstructure included vertical sides, a left-center hull placement for the driver (within a boxy structure left of the gun). The operating crew included a driver, commander, gunner and ammunition handlers. The vehicle displaced at 24 tons and sported a hull length of 24.5 feet, hull width of 9.38 feet and a full height of 8.3 feet.
Development of the GpSfl IVa proceeded though with delay. By the time an evaluation pilot vehicle was being actively manufactured, the north of France (including the capital city of Paris) had fallen to the Germans. As such, the requirement for a bunker-busting vehicle dwindled to naught. By January of 1941, the Krupp concern had completed two pilot vehicles for testing though its future would seem in doubt at this point. Its fortunes changed when, in June of 1941, the Germans invaded the Soviet Union through "Operation Barbarossa" and, while initial progress was excellent, a formulated Soviet response eventually introduced the famous T-34 medium tanks and, perhaps more importantly, the IS (Josef Stalin) heavy tank series in the IS-2.
The IS-2 was a monster of Soviet engineering combining thick armor protection reaching 120mm (4.7 inches) and a powerful 122mm main gun in a traversing turret. The vehicle had the capability to engage all manner of German types at range and posed an ever-growing threat as production and availability of the series increased. 3,854 of the type were eventually produced and these were followed by the improved IS-3 models which entered development in late 1944 though failing to see action in World War 2 altogether.
With this new threat, GpSfl IVa development continued though now under the direction that it be tested and completed as a self-propelled tank destroyer. Its tracked nature assured that it could meet cross country challenges required of the fighting in Eastern Europe and mainland Asia and its use of a standardized German Army cartridge proved logistically friendly to a resources-strapped Germany. It was envisioned that 100 vehicles would be completed in an initial batch with production set to begin in early 1942. The two pilot vehicles were placed into active frontline combat groups for formal in-the-field evaluations, this with Tank Destroyer Battalion 521.
The two vehicles were active participants along the Eastern Front against the heart of Soviet Army forces. One of the units fought on into late-1941 before it was shipped back to Krupp factories for refurbishment. Once redeployed it was eventually lost in action as the German Army began suffering through various setbacks and eventual retreats. The other pilot vehicle was not lost to enemy action, however, for an onboard fire caused by the engine consumed a propellant charge and, in turn, the vehicle was lost in a terrific explosion, the crew managing to exit their vehicle prior.
Such ended the short-lived legacy of the GpSfl IVa tank killer as only these two prototype vehicles were ever completed. Testing showcased several shortcomings in their approach: the powerplant was underpowered and made for a slow road vehicle (17mph), outpaced by the Panzer IVs (26mph) it was forged from. The superstructure was fixed in place which required that the entire vehicle be turned to face the intended target area. Not only did this consume precious fuel and oil but it applied stresses to both the engine and running gear over time which made for a less reliable vehicle. Additionally, the superstructure was thinly protected which offered little to the gunnery crew from small arms fire, the elements and air attack and there was no form of protection overhead. From what is known, there was also no active provision for a machine gun for self-defense against infantry and low-flying aircraft. Ammunition storage only allowed for 26 x 105mm projectiles to be carried into battle and this undoubtedly proved a tactical limitation for the series.
The GpSfl IVa's lone saving grace proved to be its 105mm main gun though this was not enough to save the program as a whole. The Germans found better success with the SdKfz 164 "Nashorn" tank destroyer which saw 473 vehicles produced before the end of the war. The developmental 128mm-armed "Sturer Emil" tank destroyer of 1942 also saw only two pilot vehicles produced with one destroyed by the Soviets and the other captured - yet another German tank destroyer program given up for good.
The GpSfl IVa was known under the nickname of "Dicker Max".