Project Sign
Main article: Project Sign
Project Sign in 1948 produced a highly classified finding (see Estimate of the Situation) that the best UFO reports probably had an extraterrestrial explanation. A top secret Swedish military opinion given to the USAF in 1948 stated that some of their analysts believed that the 1946 ghost rockets and later flying saucers had extraterrestrial origins. (For document, see Ghost rockets.) In 1954 German rocket scientist Hermann Oberth revealed that an internal West German government investigation, which he headed, had arrived at an extraterrestrial conclusion, but this study was never made public.