There were four series of MPC issued for use
by authorized personnel during the Vietnam War.
Series 641 (31 August 1965 - 21 October 1968)
Series 661 (21 October 1968 - 11 August 1969)
Series 681 (11 August 1969 - 7 October 1970)
Series 692 (7 October 1970 - 15 March 1973)

All MPC series consisted of seven denominations:
5¢, 10¢, 25¢, 50¢, $1, $5, and $10
The last three of the four series used in Vietnam also contained $20 notes.

MPCs are no longer legal tender but they are a popular collectors' item.