UFO propulsion and early attempts to emulate it

In a classified CIA memo dating back to 1950 that was obtained by the late John A. Keel and showcased among historic references in his book “Operation Trojan Horse”, an interesting insight appears. In the body of the typed memorandum was a reference to possible educated guesses on what could possibly propel a UFO. Electromagnetic was listed among other forms of propulsion but was crossed out by pen or pencil. Such is the case when viewing declassified documents of the US intelligence services over past decades that can actually reveal pages of blacked out text still constituting  sensitive data that cannot be revealed in FOIA requests.