What is the history of MPCs! I am in the military and never heard of them before starting to collect paper money!
Have a look here: http://www.geocities.com/scottishmoney/banknotes/usa/usampc.html They were not used after the Series 692's were withdrawn in 1973, though the Series 691 and 701 were never issued. The latter two issues were released in very small numbers to collectors in 1999 and the balance destroyed.
You can find more information about MPC at www.papermoneyworld.net. There is also a free email newsletter called the MPCGram that focuses on military numismatics which you can subscribe to by sending an email to mpcgram@yahoo.com or to stjasele@optonline.net. If you really get hooked, there is a three day convention called the MPCFest held in Ohio annually which is dedicated to military numismatics.