Your Lamp is a NATO, Sperry Block Lamp, they were specially designed for use in Searchlights and Morse Signalling Lights on Naval Battleships and Patrol Boats, I have a couple of later Thorn Halogen versions see photo.
Your Lamp is a Early Possible Osram GEC or Thorn 80 volts 1500 watts Sperry Block Incandescent Lamp, This Lamp used for Navel Searchlights and Morse Signaling Lights, NATO Ref No 6240-99-996-9809.
The Lamp I have is a Thorn HX114 230 volts 1300 watts Sperry Block Tungsten Halogen Lamp, This Lamp used for Navel Searchlights and Morse Signaling Lights, NATO Ref No 6240-99-776-4365.
Hope this Helps
All the Best
Colin