The 6-cent stamp (Scott C8) of this series was first issued on February 15, 1946, primarily for U.S. servicemen, who enjoyed a preferential six-cent airmail rate to the United States as early as January 1942. On October 1, 1946, the airmail rate was set at five cents for all customers, so the 6-cent stamps were put into storage until the rate was raised to six cents, effective January 1, 1949. The stamp is common, as are most covers, since a total of 9,440,000 were printed.
Approximately 40,500 of these stamps were overprinted for official use by Canal Zone-located federal offices (Scott CO14) between 1948 and 1951.
First day covers—many of which are known from smaller Canal Zone post offices—and single-stamp usages are quite common because the six-cent airmail rate continued in effect until August 1958. It is also found in combination with the 15-cent Gaillard Cut stamp on letters to Europe in the early 1950s, when the rate was twenty-one cents, and as a 'make-up' stamp on other covers, all of which are eagerly collected.