In the U.S. Army this technology was known as the Coincidence Rangefinder.
They were used by all the Combat Arms branches...Artillery, Infantry, and Armor, and were standard equipment on all U.S. Tanks starting with the M47 and continuing until replaced by the Laser Rangefinder in the M60A3 and M1 series of tanks.
Look for the the twin armored bulges that protect the optics. They are located on either side of the turret mid-point near the top of the turret casting on all of these tanks.
In use the Tank Commander would peer thru an eyepiece located at his station and turn a range knob until the twin images of the target appeared to "coincide" or superimpose on top of each other. When the images matched, the range could be read from the range scale and given to the gunner for use with his secondary telescopic sight, but was normally automatically fed via a mechanical linkage to the gunner's fire control computer which corrected the sight reticle in the gunners primary sight and simultaneously applied a superelevation correction to the gun mount.
Btw they worked quite well...
Steel on Target!
CptA