On June 4, 1946 Watertown was added to Colonial Airlines' Air Mail Route 71F. 

This cover was carried on the inaugural Air Mail Route 71 flight from Watertown, New York to Syracuse, new York and is listed in the Contract Air Mail Flights (CAM) Section of The American Air Mail Catalogue as 71S12.

Eastern Air Lines absorbed Colonial Airlines on June 1, 1956. Colonial Airlines had operated for more than 25 years without a passenger fatality.