This series of six airmails (Scott C15-20) marks two significant Panama Canal anniversaries—the 10th anniversary of airmail service in the Canal Zone and the 25th anniversary of the opening of the Panama Canal to ocean-to-ocean ship traffic on August 15, 1914. (The first flight was actually on February 10, 1929, with Charles A. Lindbergh in charge of the first airmail dispatch from Cristobal to Miami.) Collectors almost always refer to this series as 'The Panama Canal 25th Anniversary Airmails'. These stamps all feature an airplane of one type or another superimposed on a Panama Canal-related scene. Many of the denominations do not reflect the common rates then in use for airmail matter sent from the Canal Zone.