benEzra
Moderator Emeritus
https://en.wikipedia.org/wiki/Reflector_sight
Short version: They were invented in 1901, were in military use in World War I, and were highly developed by World War 2, but their application to small arms was limited by battery life until the development of LED's and better batteries.
Early Grubb sight (patented in 1901), which collected ambient light for the dot:
And a Mark III reflector sight from 1943 (I assume for an aircraft gun):
Short version: They were invented in 1901, were in military use in World War I, and were highly developed by World War 2, but their application to small arms was limited by battery life until the development of LED's and better batteries.
Early Grubb sight (patented in 1901), which collected ambient light for the dot:
And a Mark III reflector sight from 1943 (I assume for an aircraft gun):