The military also developed several early remote control vehicles. In World War I, the Imperial German Navy employed FL-boats (Fernlenkboote) against coastal shipping. These were driven by internal combustion engines and controlled remotely from a shore station through several miles of wire wound on a spool on the boat. An aircraft was used to signal directions to the shore station. EMBs carried a high explosive charge in the bow and traveled at speeds of thirty knots. The Soviet Red Army used remotely controlled teletanks during the 1930s in the Winter War against Finland and the early stages of World War II. A teletank is controlled by radio from a control tank at a distance of 500 to 1,500 meters, the two constituting a "telemechanical group". The Red Army fielded at least two teletank battalions at the beginning of the Great Patriotic War. There were also remotely controlled cutters and experimental remotely controlled planes in the Red Army.