Mark I Fire Control Computer

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The Mark I, and later the Mark IA, Fire Control Computer was the centerpiece of the Mark 37 Gun Fire-control system deployed by the United States Navy during World War II on a variety of ships from destroyers (one per ship) to battleships (four per ship). The Mark IA used many inputs. The target's present position relative to the ship (bearing, elevation, range) was determined by the Mk37 director mounted high on the ship's superstructure. It had optical sights and a tracking radar antenna. The director's information, called the Line-of-Sight (LOS), was continuously transmitted to the Mk 1A computer located down in the plotting room by Synchro. The ship's own motion from the gyrocompass and Pitometer log, and wind speed and direction from the ship's anemometer was also automatically entered. In "Plot", a team of operators stood around the four foot tall Mk 1A computer. Besides watching the computer's dials for proper operation, they needed to calculate and enter the average initial velocity of the shells fired from the guns before action started. This calculation was based on the powder type, the powder temperature, the projectile type and weight, and the number of rounds fired through the battery's barrels to date. Given these inputs, the Mk 1A calculates the lead angles to the future position of the target at the end of the projectile's time of flight. Meanwhile, it is calculating corrections for gravity, relative wind, and magnus effect of the spinning projectile. The lead angles and corrections are added to the Line-Of-Sight to get the Line-of-Fire (LOF). The LOF, bearing and elevation, as well as the projectile's fuze time is sent to the gun mounts by Synchro. Once the system was "locked" on the target, it produced a continuous solution to aim the guns. While the fire control systems aided greatly with ship-to-ship and ship-to-shore fire control problems, it was in the anti-aircraft warfare mode that a computer made the greatest contribution. However, the usefulness of analog computers such as the Mark I was greatly reduced with the introduction of jet aircraft, when the relative motion of the target aircraft became great enough that the gears and shafts of the computer could not keep up.