Panama Canal Zone
The Panama Canal Zone () was an unincorporated territory of the United States from 1903 to 1979, centered on the Panama Canal and surrounded by the Republic of Panama. The zone consisted of the canal and an area generally extending on each side of the centerline, excluding Panama City and Colón, which otherwise would have been partly within the limits of the Zone. Its border spanned three of Panama's provinces. When reservoirs were created to assure a steady supply of water for the locks, those lakes were included within the Zone.
Territories of the United States on stamps
The U.S. Postal Department also used general issue stamps with the territorial name overprinted, such as PUERTO RICO, CUBA, GUAM, PHILIPPINES or CANAL ZONE. Cuba was granted independence, Canal Zone returned to Panama. 
Alternatively, the U.S. issued a 1932 'United States of America' stamp for 18 centavos in the Philippines, 1930 stamps for use in Guam only designated 'Guam Guard Mail, or 1952 'Ryukyus' stamp for 100 yen in Okinawa. The Philippines was granted independence, the Ryukyus were returned to Japan. 
Panama Canal has been featured on several U. S. commemorative stamps, as well as on Panama's own postage. The territory was returned to Panama.