Railway Mail Service clerks transfer a large shipment of gold while being watched by Postal Inspectors
U.S. postal inspectors protect gold shipment to Fort Knox, 1941

Who moved the gold to Fort Knox? If you said the Post Office Department, you would be right. Under the watchful security of the Postal Inspection Service, Railway Mail Service clerks transfer some of the $9 billion in gold bullion shipped as registered mail from the New York City Assay Office to the depository at Fort Knox, Kentucky, in 1941. The Postal Inspection Service provided security and management of in the cooperative effort between the Post Office Department, local law enforcement, U.S. Army, and U.S. Treasury Department.

Courtesy United States Postal Service