Starting in 1953, East Germany received An-2 , La-9 , Yak-11 , and Yak-18 aircraft and the MiG-15bis/UTI 、MiG-17F/PF、Lim-5P、An-14A、Il-14P、Mi-9、MiG-19PM/S、Il-28、Mi-4A、Ka-26 in 1956 which were provided by the Soviet Union . The first MiG-21s were delivered in 1962. The 1970s saw the introduction of the MiG-23 , while Su-22 fighter-bombers were delivered in the 1980s. The latest addition was the MiG-29 in 1988. The inventory also included Soviet-built helicopters along with trainers and other light aircraft manufactured in Czechoslovakia .
By the 1970s, the Stasi had decided that the methods of overt persecution that had been employed up to that time, such as arrest and torture, were too crude and obvious. It was realised that psychological harassment was far less likely to be recognised for what it was, so its victims, and their supporters, were less likely to be provoked into active resistance, given that they would often not be aware of the source of their problems, or even its exact nature. Zersetzung was designed to side-track and "switch off" perceived enemies so that they would lose the will to continue any "inappropriate" activities.