The train is first seen in Episode 1 transporting troops and supplies including Private Kanata Sorami. It bears striking resemblances to the trains of the early 20th Century. Because airplanes could no longer be used due to lack in the resources to manufacture and maintain the equipment, trains continued to serve as the primary mode of transportation within Helvetia.
The train is most likely a steam-powered engine, which burns coal to boil the water for propulsion. Although it is considered primitive by 21st Century standards, trains continue to be used for transporting people and precious cargo. It also serves as the main supply line to the 1121st Platoon at Seize.