The 5-cent denomination (Scott C15) in this six-stamp commemorative series was issued with its sisters on July 15, 1939. It depicts what appears to be a DC-2 or DC-3 in flight over Sosa Hill, a landmark formation towering over Balboa and La Boca at the Pacific entrance to the Panama Canal. The west bank of the canal is easily identified on the right, and numerous ships in the approaches to the canal and the Bay of Panama islands dot the background. It is usually referred to by collectors as 'The Plane Over Sosa Hill', 'The Sosa Hill', or 'The Five-cent Anniversary Airmail Stamp'.
Some 175,000 copies of the 5-cent 'Sosa Hill' stamp were actually received, and a good number were used on first day covers. However, when the unsold remainders were destroyed in 1941, just over half of them were consigned to the fires.
This 5-cent stamp in reality paid no real airmail rate during its period of use, and it is therefore commonly found in a 'make-up' role in combination with other stamps or in multiples of three to pay a fifteen-cent airmail rate to the United States. It may also be found in any number of other roles such as on foreign covers.