Bad Aibling Station The Bad Aibling Station ( abbreviated BAS , also known as Field station 81 , which had an official designation as the 18th United States Army Security Agency Field Station , or as the pseudonym used by BND : Hortensie III ) was until 2004 a large monitoring base of the US intelligence organization NSA in Bad Aibling , Bavaria . History . In 1936 a military airfield was established by the German National Socialist government on the site of a sport airfield in Bad Aibling - Mietraching . After the Second World War , troops of the United States Army seized the military airport ( " Fliegerhorst " and flight training base ) that had evolved from the airfield . Initially , it was used by the occupying Americans as a camp for prisoners of war , a displaced persons camp , and as an orphanage under supervision of the UNRRA . Günter Grass and Joseph Ratzinger , later Pope Benedict XVI , are alleged to have met there as prisoners . In 1952 , the area was taken over by the US Army . During the Cold War it was converted by the United States Army Security Agency ( " ASA " ) to a communications monitoring station for American intelligence . In 1971 the National Security Agency ( NSA ) and the United States Department of Defense took over command from the U . S . Army . Simultaneously , the Army Security Agency transferred most of its activities in West Germany from its field station s located at Rothwesten , Bad Aibling and Herzogenaurach to Augsburg . In 1994 , the NSA transferred command of its Bad Aibling base to INSCOM , one of the Central Security Service s of USA . After the end of the Cold War , on several occasions including investigations of the European Parliament that censured industrial espionage by American secret services , the Americans intended to close the Bad Aibling Station . The September 11 , 2001 attacks delayed these plans . The restructuring of the American intelligence community after the September 11 , 2001 caused the closure of Bad Aibling Station on September 30 , 2004 . The base was returned to the Federal Republic of Germany . In the vicinity in Bad Aibling , a base of the Bundesnachrichtendienst has always been in existence within the area of former barracks of the Bundeswehr . Significance for secret services . The Bad Aibling Station was an important monitoring station of the ECHELON System ( RSOC , Regional SIGINT Operation Center ) that employed up to 1000 staff members . Its task was acquisition of information for American authorities and other closely allied intelligence services , e . g . from the United Kingdom . The López affair that was cleared up by telephone surveillance in the BAS gained worldwide audience . According to official statements , the function of BAS was " Rapid Radio Relay and Secure Common , Support to DoD and Unified Commands , Medium and Longhand Common HF & Satellite , Communication Physics Research , Test and Evaluate Common Equipment " Only few details are known . Serious hints , however , support the assumption that the BAS supervised numerous communication channels , including wireless communication , telephony and internet traffic . Particularly the communication with satellites , also outside the Intelsat system , seems to have been monitored by the BAS .