I think what you did hear was exactly what you thought it was, A millitary training excecise. I often hear Boeing Millitary Black badges or Mc Donald Douglas engineers talking to the pilots about how the craft is handling or problems that have occurred. That particular freq around here ( Wichita KS ) seems to be "clear" (very little white noise or interference) all of the time.
Just last year I heard some traffic on 4.712 usb about a KC-135 tanker plane that was loosing cabin pressure from a faulty seal around a door. They was trying to fix it in flight before they made the decision to get rid of all the fuel to make a safe landing. That day I was glued to the radio.
But back to your original question: Most of the freqs I have found in that range is mainly for Mil-Air communications. I'm sure someone will correctly ID it later but it would be a safe bet to assume that freq is reserved for Pilot to Pilot type "chatter" in order to keep the other freqs open. I've been wrong before, but never the less, 4.712 is active even here in the mid west.