The Mark 1, and later the Mark 1A, Fire Control Computer was a component of the Mark 37 Gun Fire Control System deployed by the United States Navy during World War II and up to 1991 and possibly later. It was originally developed by Hannibal C. Ford of the Ford Instrument Company. and William Newell. It was used on a variety of ships, ranging from destroyers (one per ship) to battleships (four per ship). The Mark 37 system used tachymetric target motion prediction to compute a fire control solution. It contained a target simulator which was updated by further target tracking until it matched. Weighing more than , the Mark 1 itself was installed in the plotting room, a watertight compartment that was located deep inside the ship's hull to provide as much protection against battle damage as possible. Essentially an electromechanical analog computer, the Mark 1 was electrically linked to the gun mounts and the Mark 37 gun director, the latter mounted as high on the superstructure as possible to afford maximum visual and radar range. The gun director was equipped with both optical and radar range finding, and was able to rotate on a small barbette-like structure. Using the range finders and telescopes for bearing and elevation, the director was able to produce a continuously varying set of outputs, referred to as line-of-sight (LOS) data, that were electrically relayed to the Mark 1 via synchro motors. The LOS data provided the target's present range, bearing, and in the case of aerial targets, altitude. Additional inputs to the Mark 1A were continuously generated from the stable element, a gyroscopic device that reacted to the roll and pitch of the ship, the pitometer log, which measured the ship's speed through the water, and an anemometer, which provided wind speed and direction. The Stable Element would now be called a vertical gyro. In "Plot" (the plotting room), a team of sailors stood around the Mark 1 and continuously monitored its operation. They would also be responsible for calculating and entering the average muzzle velocity of the projectiles to be fired before action started. This calculation was based on the type of propellant to be used and its temperature, the projectile type and weight, and the number of rounds fired through the guns to date. Given these inputs, the Mark 1 automatically computed the lead angles to the future position of the