A military payment certificate series 521 is a common series of military payments made during the mid- to late-1950s. A total of $317 million worth of military payments were made with this certificate series in 19 different countries, speaking to the commonality of this series.
Fifteen total series of military payment certificates were made, 13 of which were distributed. Military payment certificates were distributed from 1946 to 1973. Series 521 was the first of the series to have the note denomination printed on the back of the note, a practice that continued until the end of military payment certificates. Military payment certificates are often traded and bought as antiques.