Maps showing the area of South Vietnam north of Saigon, and the general area of operation of the 1st Infantry Division, the Big Red One.

The US military in Vietnam used paper money called Military Payment Certificates, or MPC. There were bills for all denominations, the bills were smaller than a US green back, about the size of Monopoly game money. Possession of US currency while in the county of South Vietnam, was a court martial offense, so all US money was converted into MPC when US military personnel entered the country. When items were ourchased from the Vietnamese people we usually used MPC, although such transactions were not officialy allowed. Periodically, without notice, the US military changed the bills in circulation, and all old MPC became worthless. US military personnel exchanged the MPC they had for the new bills, but the Vietnamese people that had MPC's ended up with worthless money, unless they could trade the money with someone who could exchange it for new MPC.