Somewhere not too far from where you are right now, there is a person scheming on a way to make some money. It's human nature to desire an increase in our financial status so we can acquire items that we want in life or think we need. To make this money, most people go out and find a legal job, but there are always those who look to make the easy dollar, the quick buck, regardless of the legality involved. Times of war make for several opportunities.
Summer of '67
The large aircraft finally rolled to a stop. This was it, the Central Highlands. When the door opened, all passengers filed out onto the tarmac. Dressed in rumpled khaki's and low quarters, with all our allowed worldly goods in O.D. duffel bags slung over our shoulders, we lined up for the arriving green buses. Our first indication that we were now in a world different from the one we'd left behind came as the buses quickly emptied out those soldiers going back home on the same plane we'd just arrived on. Those guys in jungle fatigues, with red mud splashed up to their knees, ran joyfully screaming and hollering toward their "freedom bird." Looked like a bad omen to us new guys.
This should give you a good idea how money itself could become a black market item, which then led to a clandestine market in money orders. Any G.I. making extra money through gambling in the barracks, becoming an entrepreneur in the underground market, or whatever illicit activity he schemed up, soon had a currency problem. Holding large amounts of MPC was no good because those bills only had value in-country. Back in the States, they were worthless. Piasters were a little shaky and not readily convertible out of the country without drawing undue attention, unless you were a legitimate business company. But, as long as a guy was careful, he could use MPC to purchase money orders at the military post office and mail them back home to the States. Trouble was, to stay out of the lime light, he had to find a lot of friends, acquaintances and/or willing G.I.'s, not also in the same trade, to make these purchases for him so his name didn't keep showing up. And, those straw-purchased money orders then had to be spread out to friends, relatives, acquaintances and/or willing G.I.'s on the receiving end to avoid suspicion from the same name always popping up as a receiver. Of course, if you could bribe the money order guy in the military post office that solved part of your problem.
Two weeks from now, more Black Market.