The Eighteen-cent Prexie
Triple six-cent airmail use
Several periods of six-cent airmail rates could have produced covers with solo eighteen-cent Prexies. Domestic airmail rates were six cents per ounce from July 1, 1934 to March 26, 1944, and again from June 12, 1947 until August 1, 1958. The six-cent concession airmail rate to and from overseas military personnel was effective from December 25, 1941 until October 1, 1946.
This triple-weight airmail letter was sent from a serviceman in Guam to Chicago in September, 1946.
This cover is problematic any way one looks at it. As a triple-weight airmail letter, the military concession rate would not apply as the armed forces member was not stationed overseas, and in June, 1945 the proper rate would have been twenty four cents. Or it could have been double-weight, with a two-cent overpayment.
Another possibility is that it was sent at six times the surface rate. This would also have been unusual, as the use of airmail envelopes for other than airmail was not allowed at that time.