Project Blue Book Case #3720. On August 23, 1955, a bright object was observed over Arlington, Virginia — the suburban county directly across the Potomac River from Washington, D.C., and home to the Pentagon, the headquarters of the United States Department of Defense. An unidentified object in Arlington airspace was, quite literally, visible from the windows of the nation's military command center.
Arlington's airspace was among the most restricted and heavily monitored in the world. Washington National Airport (now Reagan National) was immediately adjacent, and the prohibited airspace over the White House, Capitol, and Pentagon created a defensive zone that was under constant radar surveillance. Any unidentified object in this zone was a matter of the highest national security concern.
The 1955 sighting came three years after the famous July 1952 Washington radar events, when unknown objects had been tracked over the capital on two consecutive weekends, generating worldwide headlines and the Air Force's largest press conference since World War II. Another unknown in virtually the same airspace — though apparently not as dramatic as the 1952 events — demonstrated the persistence of the phenomenon.
The object could not be identified despite the comprehensive radar coverage and air traffic control monitoring that blanketed the Washington metropolitan area. Every aircraft in this airspace was tracked and identified as a matter of course — yet this object eluded that identification.
The case was classified "Unknown" — a remarkable determination for a sighting within sight of the Pentagon.