Ive acquired this from an old RAF stash they found near Carlisle:
From what I can gather its a receiver for the old decca navigation, on the "purple" wave band and it worked out an aircraft's position by the phase different from the beacons that made up the decca system. Apparantly it was fairly standard fit on some RAF aircraft in the 50's and 60's before INS took off.
I bought the green one from the Solway Avitation Museam in Carlisle airport, with the same black paint on the back (mine is less damaged then yours though - it still has all the knobs attached!).
