When you're on a destroyer steaming full speed through the North Atlantic firing at an enemy ship 15,000 meters away that's trying its best to sink you, you'd better make well sure your shot hits first. To ensure our sailors stood a fighting chance during WWI's intense naval engagements, the DoW built and outfitted America's fleet with some of the world's first fire control computers.

Hitting a moving target with a projectile is not as easy as it looks, especially not at sea where you have to not only account for wind speeds and directions but also take your target's course, distance, and speed (as well as your own vessel's), not to mention the fact that the rolling of the waves continually throws off your sighting. And as the caliber of naval guns increased during the leadup to WWI, so too did their firing range, which led to increasingly complex (and slower) calculations.

To speed that process up, the British Royal Navy in 1912 centralized the firing process. As Spectrum IEEE explains:

All the guns on a ship were directed from a single position (usually the highest part of the ship). The fvused a T-shaped optical rangefinder containing prisms to ascertain the distance, bearing, and change-of-bearing to the target by means of triangulation. The fire-control officer then communicated—usually via telephone, but with voice tubes as backup—this information to the sailors in the control center deep in the ship. They in turn moved cranks and levers to input the information into large mechanical calculators (some the size of three or four refrigerators), which used this constantly changing data to plot firing solutions for the guns. The guns would then be fired in salvoes, with a slightly different trajectory from each gun, thereby increasing the chance of hitting the target.

This method extremely effective and quickly made its way to this side of the Atlantic. By the onset of WWII, America's Navy had developed a similar system: the Mark 1 Fire Control Computer.

​It's a Miracle WWI US Naval Destroyers Managed to Hit Anything at All

The Mark 1 Fire Control Computer was a vital component of the navy's Mark 37 Gun Fire Control System and, for more than three decades served as the fleet's primary means of calculating shots at sea. While it was smaller than the earlier British design, the Mark 1 was still a hefty piece of equipment standing four feet tall and weighing more than 3000 pounds. And, given its importance, was similarly stored in the bowels of the vessel where it would be most defended against battle damage.

The Mark 1 is classified as an electromechanical analog computer—not quite digital yet but leagues beyond an abacus and slide rule. The gun director unit (an electronic device that served the same function as the earlier fire-control officer and rangetakers) topside would gather optical and radar telemetry information—known as Line of Sight (LOS) data. The director unit would then transmit the LOS data via a series of synchro motors down to the Mark 1 which would subsequently calculate out firing instructions and the necessary lead angles based on the two ships' movements through the wateras well as environmental factors like gravity and relative wind. This analyzed data, known as the line-of-fire (LOF) data, would then be transmmitted up to the gun batteries throughout the vessel to line up the next shot. And as soon as the first set of calculations were complete, the system effectively "locked on" to a target and continually rain hot lead without the need to keep redoing the calculations.

This system worked wonderfully—especially against aircraft—until the advent of the jet engine, which allowed warplanes to travel faster than the Mark 1 could calculate trajectories. This essentially negated the Mark 1's lock-on capability and severely reduced its effectiveness after WWII. The Navy did upgrade the Mark 1 with more advanced electronics just after the war but wound up replacing the outdated system entirely in the early 1970s upon the advent of digital fire control systems. [Wiki - HNSA - IEEE]