On September 23, 1978, the USPS issued the first stamps in its Pioneers of Aviation Series. The series would span more than 20 years and include 18 stamps honoring some of America’s most legendary aviators and their aircraft. The stamps in the series covered the international airmail rate. The first few stamps maintained a similar size and style, but that would change over the course of the series. All the stamps featured the aviator and the plane with which they were most closely associated. And most included phrases such as “Aviation Pioneer” or “Pioneer Pilot.”