His early research into meter-wave propagation and radar beams necessitated additional names for newly discovered levels of the Earth's atmosphere, and Plendl is generally credited with coining the term ionosphere.
As Nazi Germany rearmed, Plendl and others saw the possibilities of using radio beams to guide bombers to their target, and they began to develop a system under the code name "X-System" (X-Verfahren).
[4] Both systems employed transmitter towers on the English Channel and the North Sea to transmit radar beams over targets in England.
Sources differ as to why he was dismissed, including that it was after a heavy raid upon Hamburg where the British used a special counterradar technique called Window or chaff,[9] or was due to his saving several people from death in concentration camps, by claiming he needed their (non-existent) "expertise" to help his beam program.
Particularly noteworthy was the fact that Plendl had saved a number of people, including many Jews, from the Dachau concentration camp, under the guise of needing them to work on his projects[14] Many of these individuals had no scientific background.
Plendl helped Karl-Otto Kiepenheuer establish a Europe-wide network of stations observing the solar activity in order to predict disturbances of the Ionosphere that interrupted the military radio connections.
Plendl and Kiepenheuer may so be seen as the fathers of the science now called space weather, A considerable part of their network prevailed after the war in one or another organisation.
Jones, the British scientist who had worked on the other end of the channel to jam Plendl's beams, became a good friend, and the two corresponded regularly and collaborated on several books.