[MilCom] What is it?

[WB6BLV (DM06)]

Some years ago I picked up some unopened boxes of military surplus units.
The boxes were labeled  Audio Frequency Amplifier AM-1415/USN-I and the one
I opened contained what appeared to be an audio amplifier bolted to a piece
of 3/4 inch plywood.  Two of the front panel controls were for an "Alarm'
function.    The ID plate on the amp carries the same inscription as that
stencilled on the outside of the box.  Anybody on the list recognize what
these things were for?

John