By the start of the twentieth century, it was clear that armoured vehicles were more than just a novelty. In the sea, the introduction of the ironclads - impervious to cannon of its era - soon led to a rapid arms race. An equivalent on land, however, was then impossible, for such heavy armour could only be transported by rail. In 1903, British inventor Bramah Joseph Diplock invented the pedrail -- a system of mechanical "feet" on which an engine may walk. It soon became clear that the improved mobility this offers with respect to wheels allows a locomotive to be constructed that is capable of traversing a large variety of terrain. To this end, a "land ironclad" was designed, to be constructed variously of riveted steel and cast iron. Much like the pioneering USS Monitor, a powerful cannon -- the Ordnance BL 12 pounder 6 cwt -- was mounted in a cylindrical turret allowing complete rotation. Two side pods holding lighter 3 pounder guns were included to augment firepower against infantry. As for propulsion, the obvious choice of the era was the steam engine, capable of the prodigious amounts of torque requisite to move the metal behemoth. A large boiler in the rear was connected to reciprocating pistons powering the left and right pedrails independently, so as to enable steering. The North British Locomotive Company, which was then newly created and largest in Europe, was commissioned to construct a prototype -- Locomotive No. 19407. This prototype was purportedly completed in 1906, coinciding with the launch of the HMS Dreadnought, a landmark of equal importance in naval affairs. However, it was lost as it attempted to traverse some marshes and sank into a bog. Due to the lack of complete documentation, the vehicle faded into obscurity and myth. The tank concept would not be implemented again until 1914 with the British landship programme, which ultimately culminated in the Mark I tank.

More information: The gunner looks through the circular porthole on the front of the turret -- dubbed the "monocle" by the crew. The three men in the turret rotate it by hand-cranking it. The driver, who gets to see the outside through the three circular windows, works closely with the fireman who feeds the coal into the boiler at the rear. Coal is stored in the front. Water is stored on either side of the boiler. The fifty-tonne behemoth rides on twenty-two coil springs. The springs on the pedrails - ninety-two in total, one pair for each of the forty-six "feet" - are not load bearing and exist only to orient each foot in the correct angle. Because of the dome on the boiler behind the turret, the turret cannot be traversed completely without elevating the gun to clear the dome. However, this was not considered a major issue because Locomotive NO. 19407 is not intended to operate solo; instead, it is meant to be heavily supported by infantry, especially in breakthrough operations, as a mobile field gun.