The last stamp in the Transport Plane Series, the 8-cent airmail stamp was issued primarily to pay the new eight-cent-per-ounce domestic airmail rate that became effective March 26, 1944. It was printed in an olive green color. The eight-cent-per-ounce rate applied to airmail within the United States as well as mail to and from Alaska.
Because airmail was still relatively expensive in the early 1940s, especially international airmail rates, some letters were sent by a combination of part surface and part airmail. For example, while airmail all the way to Hawaii from the U.S. was twenty cents per half-ounce, for postage of eight cents one could send a letter by airmail from New York to California, thence by surface (ship) to Hawaii, thereby reducing the mail in transit time by about two days from the least costly all surface means.
The new eight-cent rate and not the special six-cent military rate applied to military personnel stationed in the U.S. as of March 1944. While military personnel abroad were given a special six-cents-per-half-ounce airmail rate during all of WW II (otherwise much higher civilian airmail rates—as high as $1.10-per-half-ounce—would have been required), military personnel stationed in the continental U.S. paid the higher eight-cent-per-ounce rate, the same as civilians.