Hey Mubutu,
Could you check if there is a serial number on this part, but the one on the front end:
It is possible that the "255" refers to U-255, which was surrendered intact to the British.
I also found similar pair of UZO numbered with "4" (U-4 survived the war, was scrapped) and "19" (U-19 was scuttled in 1944, makes sense to take such equipment with you).
Though, I also found "1328", which doesn't match any known U-boats.
The "hell/dunkel" switch is for bright/low light conditions.