With the Industrial Age (1820-1840) came about a vast expansion of the railroad industry and this meant networks of track laid down to connect major cities and regions to one another. Journeys that once would have taken weeks to months on roads took only weeks to days. The American Civil War (1861-1865) was the first conflict to truly prove the train as a viable battlefield component - useful in ferrying troops and war goods to-and-fro. During World War 1 (1914-1918), the train took on a more purpose-built concept in some examples being armored and armed to serve in direct-combat or support roles. While limited in their reach by the existing network of track, the armored train nonetheless proved its worth to the point that all of the major Empires of the period employed the type in some form or another. By the time of World War 2 (1939-1945), the armored train evolved some but retained its basic value.
In 1943, with World War 2 in full swing, the Germans commissioned Steyr-Daimler-Puch to design, develop and produce a new heavy-class armored rail cruiser for scouting and denial duties. The class was to utilize components from existing platforms and make up the "Schweren Schienenpanzerspahzug" (s.Sp.) armored scout train. For instance, the main armament, turret and all, was taken from the large stock of Panzer IV Medium Tanks. These turrets were simply set about a crude, angled armored superstructure. The superstructure was them superimposed atop an existing railway car.
Machine guns could be fitted along crucial facings and operated from within the cars, gunners utilizing vision slits to engage. The placement of the turret atop the superstructure allowed for a full 360-degree traversal to be had though the short 75mm gun form of the Panzer 4 tank series were used due to availability. However, these weapons still packed a punch, particularly when HE (High-Explosive) shells could be used against "soft" targets. A purpose-built "command car" - with room for infantry squads - could be attached to this "gun car" and the units were either self-propelled or attached to a locomotive as needed. Other support cars could then be attached to the group to form a mighty roaming "fortress-on-wheels"- completing the Schweren Schienenpanzerspahzug.
In practice, the self-propelled railway car was used to reconnoiter positions near contested ground or support ongoing infantry actions by bringing large-caliber guns to bear against unsuspecting elements. Denial of strategic rail junctions and bridges could also be had as the cars could be moved anywhere the rail network allowed. Of course all this changed the moment an Allied bomb or demolition charge ruined the tracks - then denying the cars advancement of any kind.
The Schweren Schienenpanzerspahzug concept began construction in May of 1944 and entered service around November of that year. Of the sixteen complete systems planned, just six were realized and these were operated into April of 1945 - the final month of the war in Europe. If not taken as war prizes, the cars were stripped of their war-making usefulness and scrapped.