The 25-cent stamp (C-18) from this six-stamp series was intended for use as 'make-up' since there was almost no real twenty-five cent rate to any foreign destination at the time. The series honored the 10th annivesary of airmail service in the Canal Zone as well as the 25th anniversary of the opening of the Panama Canal. The stamp depicts what seems to be an undersized Pan American clipper flying boat landing at Cristobal on the Atlantic side of the Canal Zone, where the seaplane terminus was located. Many collectors commonly refer to this issue as merely 'The Twenty-fifth Anniversary 25-cent Airmail'.
Exactly 200,000 copies of the 25-cent airmail were shipped to the Isthmus, but only slightly over 82,000 were sold. The unsold stamps were burned on April 12, 1941.
Many of the 25-cent stamps were used on first day covers either singly or in combination with other stamps from this series. Non-philatelic examples of this stamp are avidly collected, usually in the form of letters to foreign addresses or for special occasions such as registration or on overweight letters.