Fire Control: Rangefinders, Use
"Rangefinders functioned in one of two ways: coincidence (invented 1885) and stereographic (invented 1893). Coincidence rangefinders split an image into two, so the operator had to line up the top of the image with the bottom (image 1 is an example of this 'cut' view). In stereo rangefinders, two images were produced (see image 2) - the user had to align them. In each case, the device calculated the range based on how much adjustment was required. This reading would then be passed on to someone/something that could make sense of the data and translate it into gun elevation and direction (train).
Originally, rangefinders were placed on turrets or near the conning tower to ensure that range data was passed with minimal delay. But, this limited how far the device could see. This was fine at first - guns could not yet fire to the horizon as seen from masts. But by the end of WWI, range was only practically limited by rangefinder height and gun elevation. Rangefinders were increasingly mounted higher.
They also became more numerous. Ensuring data accuracy was key - averaging readings from rangefinders throughout the ship would provide the most accurate data, and quickly catch errors. So, ships of the 1910s featured them all over; mastheads, platforms, bridge wings, conning towers, on, and in the turrets. Bridge units could be used for situational awareness, while turret units aided independent firing at short range.
Originally rangefinders were just a stand with an optics tube on it. But, war experience showed the importance of protecting their operator(s) ; initially this was just light splinter shielding (photo 3 of Omaha, CL-4), but evolution turned these into revolving, powered enclosures with additional equipment and protection. Multi-function enclosures would become known as directors, essentially a master gunsight for the ship, but that is for another post.
Rangefinder data had to be tracked to predict target location at a future moment. The device needed to manage this sort of data was the rangekeeper, to be covered next."
For a MUCH more detailed post, subscribe via https://www.patreon.com/hazegreyhistory. Caption is exclusive to Haze Grey History Facebook page (link) and was shared with the permission of Evan Dwyer. Click this link to read more of his works.
