50 Cents Military Payment Certificate

Series 681 MPCs were issued in August 1969 as part of a surprise "C-Day" currency conversion in Vietnam — all previous series were declared void within hours, a deliberate tactic to trap black market operators and currency speculators holding large undeclared stocks. Soldiers had a single day to exchange their old certificates; Vietnamese nationals and anyone outside authorized channels was left holding worthless paper.

The 50-cent denomination was a workhorse of the MPC system, used heavily in base canteens and clubs where fractional transactions were common. Series 681 was withdrawn in November 1970 under the same abrupt conversion procedure.