Nauen Transmitter Station (German: Grossfunkstelle Nauen or Sender Nauen) in Nauen, Havelland district, Brandenburg, Germany, is the oldest continuously operating radio transmitting installation in the world. Germany's first high power radio transmitter, it was founded on 1 April 1906 by Telefunken corporation and operated as a longwave radiotelegraphy station through World War II, and during World War I became Germany's main link with the outside world when its submarine communications cables were cut. Upgraded with shortwave transmitters in the 1920s it was Germany's most advanced long range radio station, continually upgraded with the latest equipment and serving as an experimental station for Telefunken to test new technology. At the end of World War II, invading Russian troops dismantled and removed the transmitting equipment. During the Cold War it served as the GDR's (East Germany's) international shortwave station Radio Berlin International (RBI), and was the East Bloc's second most powerful radio station, disseminating Communist propaganda to other countries. Since German Reunification in 1991 it has been operated by Deutsche Telekom, Germany's state telecommunication service. The original 1920 transmitter building designed by architect Herman Muthesius is still used; it is the only remaining building designed by that architect.