Project Blue Book Case #1011. On December 18, 1951, an unidentified object was observed over Andrews Air Force Base — the installation that served as the home base for Air Force One and the primary military airfield for the Washington, D.C., area. An unknown over Andrews was an unknown over the President's own runway.
Andrews sat in Prince George's County, Maryland, just southeast of the capital. Its airspace was part of the most restricted and heavily monitored zone in the country. The base would play a central role in the famous July 1952 radar events, when its radar tracked unknown objects over Washington — but this December 1951 sighting predated those famous events by seven months.
The appearance of an unidentified object over the presidential air base was a security incident of the highest order. Andrews' radar and security systems were comprehensive, and every aircraft in the Washington area was tracked and identified as a matter of routine.
December 1951 came during the transitional period between Project Grudge and Blue Book. The case was classified "Unknown" — a precursor to the much more dramatic Andrews events that would unfold the following summer.