The armored train concept was not a new one by the time of World War 1 (1914-1918) for the American Union Army made use of such systems in the Civil War against the Confederates to help protect vital railways and key bridges from destruction. However, by the time of The Great War, the concept had evolved considerably through initially crude developments and, later, more standardized approaches. Armored trains were just that, trains clad in armor protection and fielding artillery-level firepower while defensed by machine guns. Some systems incorporated special infantry cars for foot soldier support. In this way, the mobile firing platforms could be brought to bear in a nearby engagement while the foot element went ahead to tackle enemy infantry as found or scout out positional ambush positions. Still other doctrines incorporated cavalry forces which could be unleashed alongside the infantry all while under the protective fire of the armored train.
Despite its slow modernization during the Industrial Revolution, it was the Russians that led the charge in unique and standardized armored trains. Other world powers followed suit however, including Austro-Hungary, the German Empire and the British. The Austro-Hungarians developed their Panzerzug I (PzZug I) as a solution in 1914. Its construction was undertaken by Hungarian railways producer Magyar Allamvasutag (MAV) who used one of its own locomotives for the drive. Its manufacture occurred from 1914 into 1915 and included a specially-designed gun car, the locomotive and several infantry cars.
However, it was not until the succeeding model - the Panzerzug II (PzZug II) that a viable form was achieved. Construction moved swiftly amidst the bogged down nature of the war now reduced to trench networks. By 1916, MAV had completed ten units for operational service and these went on to fight across the Russian Front as well as those in Italy and Romania.
PzZug II was of note for the Austro-Hungarian Army for it laid the ground work for subsequent designs that followed by supplying the general approach to their armored train designs. While the train system could be of any length depending on the mission, it was typical to see it in a three-car arrangement with a gun car at front, the locomotive at center and an infantry machine gun car at rear. The forward gun car showcased a turreted 70mm gun to content with enemy artillery concentrations and fortifications. A high cupola with vision slits capped the armored superstructure aft of the turret emplacement. Defensive-minded machine guns managed the sides of the cars. A simple four-wheeled design was used across all gun cars in the line. The locomotive was of a conventional arrangement for the period with its front-mounted smoke funnel. The wheel house as aft and fully protected in plate armoring with vision slits for situational awareness and access doors that could be closed when under fire. The locomotive proved a six-wheeled unit. At the end was the infantry car fielding portholes along its sides for machine guns. This car was principally used to protect the train from infantry attack through machine gun suppression.
In practice, such developments were used to support infantry forces as far as the train's artillery systems could reach. They additionally proved useful in defense of key areas including bridges and forward bases and could be uses in patrolling and reconnaissance actions where rail lines provided the access. Not inherently fast, these trains were still mobile firing platforms akin to a tank or warship - and a single armored train could very well change the direction of a fight in seconds. Many commanders of the period certainly held armored trains in high regard for their ferociousness in-the-field and imposing design appearance.