Fahrpanzer The Fahrpanzer was a mobile artillery piece made prior to World War I in Germany , implemented in several German fortifications from 1890 onwards and exported to several foreign military powers prior to the outbreak of hostilities . Specifications . As designed the Fahrpanzer was mounted on narrow gauge railroad trucks and was wheeled along 60 cm tracks to its battle station . When not in use it would be pushed into a protective bunker to avoid damage during heavy bombardment . The Fahrpanzer was not autonomous : as originally designed it could only be pushed into place and rearmed from outside . It is not clear whether in practice any Fahrpanzer were retrofitted to be self - propelled or self - reloading . However artillery pieces of any kind were in short supply during World War I , and many Fahrpanzers were removed from their fortifications and installed in forward trenches by the Germans . For road transport the Fahrpanzers had purpose - built horse - drawn carriages . All export models of the Fahrpanzer were sold with such a carriage , and it appears some export Fahrpanzer remained affixed to their carriages for the duration of their military career . All Fahrpanzer were fully armored and operated by a two - man crew . They may have been positioned and rearmed by the gun crew , or by handlers stationed outside the weapon . In any event the lack of self - propulsion and self - rearming capability placed its operators at risk . The Fahrpanzer could have benefitted from continued development to equip it with such capabilities , however the emergence of fully autonomous armored tanks on the battlefield effectively rendered the concept obsolete . A period illustration clearly showing several remote - controlled , machinegun armed Fahrpanzer engaged in trench warfare does exist , however no photos or documents exist to suggest the idea ever evolved past the conceptual stage . Armament consisted of one Grunson 5 . 3 cm quick - fire gun capable of + 10 degrees and minus 5 degrees elevation , mounted in a 360 degree rotating turret . The gun could fire a 1 . 75 kg shell with a muzzle velocity of 495 m / s , and fire a maximum of 30 shells per minute . The shells were fed from inside by the two - man gun crew , who would be fully protected by the Fahrpanzer ' s armor until it ran out of ammunition . In practice the firing of the gun destabilized the Fahrpanzer badly , reducing the accuracy of the crew ' s aim . The Fahrpanzer on display in the Army Museum in Brussels has long been cited as the only remaining example , however pictures of restored Fahrpanzers can be found originating from Bulgaria , Greece , Switzerland and South America . There are also numerous Fahrpanzers on display in the Polish Army Museum and Museum of Polish Military Technology , both in Warsaw . Romania purchased 334 Gruson Fahrpanzers , in the 53 mm caliber . These were initially deployed on the Siret Line at Focşani ( 15 batteries , with 6 turrets each ) , Nămoloasa ( 24 bateries of 3 - 5 turrets ) , Galati ( 30 batteries of 6 turrets and 10 bateries of 3 turrets ) and Brateş ( 10 turrets ) . The bridgeheads ( not part of that Line ) at Cernavodă and Turtucaia were equipped with 28 turrets , and the one at Silistra was equipped with 17 turrets . These guns remained in their emplacements for about twenty years , before being transformed in infantry guns between 1914 and 1916 by mounting them on Romanian - built gun carriages . A few were transformed in anti - aircraft guns .