WillDAQ
When Reaction Engines developed it.
Then how is it that Paul Czysz talked about a proposal from McDonnell/McDonnell-Douglas cooling airflow into a gas-turbine, while simultaneously increasing the RPM as the mach number increases (Mach 6, IIRC)?
While I'm not sure if the proposal he was talking about included a precooler or a MIPCC scheme; regardless, there is the Japanese ATREX which also made extensive use of an advanced pre-cooler.