What it is?

[sheepherder]

The Germans also had an infra-red light & sight combination they called "Vampir" (which was later copied by the US and mounted on an M1 Carbine). "Vampir" used a backpack battery and umbilical leads for the light/sight. I used to have pics of that setup but that was decades ago.

The battery pack for the Luger would have been interesting. The bulb is huge (there is a separate picture of it in TBLAP under Dead Ends & Curiosa) and there is no description of whether the 'barrel' of the light uses a mirror or prism or direct impingement to direct the bulb's light out.

Another idea ahead of its time.

(Pic is of captured "Vampir" not showing huge backpack-battery)