The 30-cent stamp (C19) from the 25th Anniversary series was issued on July 15, 1939, as one of six stamps honoring the 10th anniversary of airmail service in the Canal Zone as well as the 25th or Silver Jubilee of the opening of the Panama Canal. It depicts a Pan American clipper flying boat over the Continental Divide at the Gaillard Cut with a battleship and three smaller vessels in transit of the Canal en route to the Pacific Ocean. Collectors commonly call this stamp the 'Clipper Ship Over Gaillard Cut Airmail'.
Some 270,800 of this stamp were printed, but only just over 121,000 were sold before the remainders were burned on April 12, 1941, after being pulled from post office drawers on February 28th.
A relatively large number of these stamps were used on first day covers, most frequently in combination with the other stamps of this series. A 30-cent stamp would pay postage on a double-weight letter to the United States or a single-weight registered letter. Other usages are found in multiples or different stamps in a 'make-up' role. All are avidly collected.