Issued in Washington, D.C., on June 25, 1941, the carmine 6-cent value airmail stamp was the first in the Transport Plane Series. It paid the six-cents-per-ounce domestic airmail rate (within the continental U.S. including Alaska) which had been in effect since July 1, 1934. It also paid the airmail rate to Canada, which was charged the same rate as U.S. domestic airmail during this period.
Following the U.S. entry into World War II, the 6-cent Transport airmail stamp received increasingly heavier usage. Beginning December 25, 1941, a special military concession airmail rate of six-cents-per-half-ounce became available to or from U.S. Armed Forces personnel stationed outside the continental United States. The civilian airmail rates, which ranged from ten cents to $1.10 per half-ounce, had previously applied. Most of this military-related airmail was sent from (and also to) APOs (Army Post Offices) or FPOs (Fleet Post Offices) both overseas and within the U.S. Over 4 billion, 746 million copies of this 6-cent Transport plane airmail stamp were printed, making it the second largest printing in the history of U.S. airmail stamps.