See inside a secret Navy museum on an active base where visitors require an official escort at all times

• The National Museum of the US Navy is located in the Washington Navy Yard, an active military base.
• Access is limited and security measures are tight, but it contains fascinating artifacts.
• Exhibits include the USS Constitution mast and part of the submersible that found the Titanic.

Before I could join a dozen others for a tour of the Washington Navy Yard in Washington, DC, I first had to pass through its heavily guarded gate.