During World War I, the British built two armored trains. One was to protect the East Anglian coast from the German Navy, and the other was to protect the east coast of Scotland. Several train companies worked together to supply the required component parts. Great Northern Railways supplied the engines which were positioned in the middle of the trains. The engines were 0-6-2-type tank locomotives, the kind that are now used on the District Line of the London Underground. Everything above the frame was protected with armor plating. The cab windows had sliding metal shutters.
The plan was for the trains to speed to the location of a German invasion, deploy troops and back them up with artillery fire from the large guns at either end of the trains. This would slow the enemy down until support could arrive.
The infantry vans were supplied by the Great Western Railway. They were converted 40-ton coal wagons with half-inch-thick armor on the sides and three-eighths-of-an-inch armor on the roof. Enlisted men rode in an open carriage, with a coal bunker under the floor, drinking water tanks and a stove. Officers had partitioned quarters. There were rifle loops on both sides of each troop wagon.
The stand-out feature of each train were the two gun wagons, one at the head and one at the tail of each train. The Caledonian Railway supplied each gun wagon. They had three compartments, the Maxim gun configuration at the end nearest the engine, the ammunition compartment in the middle, and the main gun compartment was at the far end.
The only part that was not supplied by the railways, was the guns. The main gun was a 12-pound rapid-firer. The gun was mounted between the carriage bogie wheels. This distributed its weight and kept the guns’ recoil from derailing the wagon. Each gun wagon had an office for the train’s commanding office. The Maxim gun had 3,000 rounds and a water tank to cool the gun down, The Engineer reported.
While most steam trains of the era were operated from the footplate, the armored trains had to rig something else up. Since the engines were in the middle of the trains, the engineer’s view was blocked. So they configured an intermediate valve alongside the smokebox. A link and lever actuated by a vacuum cylinder on the engines footplate. The engineer then stood at the end of the train and communicated with the fireman by telephone.