50 Cents Military Payment Certificate

Series 681, which M-81 belongs to, was issued in August 1969 and retired in a surprise "conversion day" on October 7, 1969 — a covert operation in which all personnel were given a matter of hours to exchange old scrip for Series 692. The abrupt changeover was deliberately designed to trap black-market operators and Vietnamese civilians holding MPC illegally, rendering their stockpiles worthless overnight. American service members were notified only at the last moment, which caused genuine hardship for those on leave, hospitalized, or in the field.

Series 681 consequently circulated for under two months.