The Fahrpanzer is a German mass-produced, modular, mobile pillbox from before the Weltkrieg, armed with a 57mm quick-firing cannon, which can be replaced for another light artillery piece or a machinegun. It is encased in steel and contains its own ammunition supply. The Fahrpanzer can only be transported from the outside by cart or motor vehicle, and resupply is a dangerous task, as the operators must open its hatch to introduce ammunition. Hundreds were built and exported worlwide, including to the fortified city of Sydney, from which the design spread throughout the nation.