There is a great deal of mysterious information surrounding this submachine gun. A few things are certain: it was designed by Juan Erquiaga Azicorbe, a former Peruvian army officer and immigrant to the USA. It was designed in the early 60's and manufactured in 1964, with over 1000 models being made at the Erquiaga Arms Company in the City of Industry, California. Gordon Ingram, who was then working at the Police Ordnance Co., was involved in the design of the MR-64 and was friends with Erquiaga. I suspect Ingram met Erquiaga during the lengthy period of time he spent in Peru whilst working for the Police Ordnance Co., setting up production for his Model 6 submachine gun.Production ended in 1965 when Erquiaga's factory was raided by the FBI and most of the weapons and ammunition being produced there were confiscated or destroyed. Allegedly he was attempting to arm a "private army" of Costa Ricans and Cubans, who were supposedly fighting against Fidel Castro (some sources state that Erquiaga was actually making guns for Castro; this is probably a mistake). He also made silencers for these guerillas. Details in this area of the story are shallow, although whatever the intended purpose for the weapons, they were being manufactured illegally and the whole ordeal forced Erquiaga to flee back to South America. What happened to him after that is not known.