During the Vietnam War, it was illegal to possess hard currency (green dollars, postal money orders, marks, francs, etc) so all military personnel (including US, Australian, and Korean soldiers) were paid in MPC. Payments were limited to $200/month and expenditures could not exceed that same amount. Tracking of these transactions was done by computers and voluminous printouts identified those personnel who were violating this ordnance and that info was then sent to the various Military Police and CID units for further investigation.

The example above is a counterfeit $10 bill. Counterfeits were relatively common.