Wikipedia
Rangekeepers were electromechanical fire control computers used primarily during the early part of the 20th century. They were sophisticated analog computers whose development reached its zenith following World War II, specifically the Computer Mk 47 in the Mk 68 Gun Fire Control system. During World War II, rangekeepers directed gunfire on land, sea, and in the air. While rangekeepers were widely deployed, the most sophisticated rangekeepers were mounted on warships to direct the fire of long-range guns.
These warship-based computing devices needed to be sophisticated because the problem of calculating gun angles in a naval engagement is very complex. In a naval engagement, both the ship firing the gun and the target are moving with respect to each other. In addition, the ship firing its gun is not a stable platform because it will roll, pitch, and yaw due to wave action, ship change of direction, and board firing. The rangekeeper also performed the required ballistics calculations associated with firing a gun. This article focuses on US Navy shipboard rangekeepers, but the basic principles of operation are applicable to all rangekeepers regardless of where they were deployed.