Fire-control system

[1] Even during the American Civil War, the famous engagement between USS Monitor and CSS Virginia was often conducted at less than 100 yards (90 m) range.

These guns were capable of such great range that the primary limitation was seeing the target, leading to the use of high masts on ships.

Corrections are made for surface wind velocity, firing ship roll and pitch, powder magazine temperature, drift of rifled projectiles, individual gun bore diameter adjusted for shot-to-shot enlargement, and rate of change of range with additional modifications to the firing solution based upon the observation of preceding shots.

[1][3] Between the American Civil War and 1905, numerous small improvements, such as telescopic sights and optical rangefinders, were made in fire control.

[4] Then increasingly sophisticated mechanical calculators were employed for proper gun laying, typically with various spotters and distance measures being sent to a central plotting station deep within the ship.

Pollen began working on the problem after noting the poor accuracy of naval artillery at a gunnery practice near Malta in 1900.

[7] Lord Kelvin, widely regarded as Britain's leading scientist first proposed using an analogue computer to solve the equations which arise from the relative motion of the ships engaged in the battle and the time delay in the flight of the shell to calculate the required trajectory and therefore the direction and elevation of the guns.

Pollen aimed to produce a combined mechanical computer and automatic plot of ranges and rates for use in centralised fire control.

[9] During their long service life, rangekeepers were updated often as technology advanced, and by World War II they were a critical part of an integrated fire-control system.

The incorporation of radar into the fire-control system early in World War II provided ships the ability to conduct effective gunfire operations at long range in poor weather and at night.

Directors high on the superstructure had a better view of the enemy than a turret mounted sight, and the crew operating them were distant from the sound and shock of the guns.

Unmeasured and uncontrollable ballistic factors, like high-altitude temperature, humidity, barometric pressure, wind direction and velocity, required final adjustment through observation of the fall of shot.

Submarines were also equipped with fire control computers for the same reasons, but their problem was even more pronounced; in a typical "shot", the torpedo would take one to two minutes to reach its target.

The battleship USS North Carolina during a 1945 test was able to maintain an accurate firing solution[12] on a target during a series of high-speed turns.

The effectiveness of this combination was demonstrated in November 1942 at the Third Battle of Savo Island when the USS Washington engaged the Japanese battleship Kirishima at a range of 8,400 yards (7.7 km) at night.

[14] The Japanese during World War II did not develop radar or automated fire control to the level of the US Navy and were at a significant disadvantage.

An early use of fire-control systems was in bomber aircraft, with the use of computing bombsights that accepted altitude and airspeed information to predict and display the impact point of a bomb released at that time.

Simple systems, known as lead computing sights also made their appearance inside aircraft late in the war as gyro gunsights.

These devices used a gyroscope to measure turn rates, and moved the gunsight's aim-point to take this into account, with the aim point presented through a reflector sight.

Small radar units were added in the post-war period to automate even this input, but it was some time before they were fast enough to make the pilots completely happy with them.

The LABS system was originally designed to facilitate a tactic called toss bombing, to allow the aircraft to remain out of range of a weapon's blast radius.

The principle of calculating the release point, however, was eventually integrated into the fire control computers of later bombers and strike aircraft, allowing level, dive and toss bombing.

The early versions of the High Angle Control System, or HACS, of Britain's Royal Navy were examples of a system that predicted based upon the assumption that target speed, direction, and altitude would remain constant during the prediction cycle, which consisted of the time to fuze the shell and the time of flight of the shell to the target.

The USN Mk 37 system made similar assumptions except that it could predict assuming a constant rate of altitude change.

The Kerrison Predictor is an example of a system that was built to solve laying in "real time", simply by pointing the director at the target and then aiming the gun at a pointer it directed.

[21] Early systems made use of multiple observation or base end stations (see Figure 1) to find and track targets attacking American harbors.

They are typically installed on ships, submarines, aircraft, tanks and even on some small arms—for example, the grenade launcher developed for use on the Fabrique Nationale F2000 bullpup assault rifle.

Fire-control systems are often interfaced with sensors (such as sonar, radar, infra-red search and track, laser range-finders, anemometers, wind vanes, thermometers, barometers, etc.)

Typically, weapons fired over long ranges need environmental information—the farther a munition travels, the more the wind, temperature, air density, etc.

A German anti-aircraft 88 mm Flak gun with its fire-control computer from World War II. Displayed in the Canadian War Museum .
Admiralty Fire Control Table in the transmitting station of HMS Belfast .
Ford Mk 1 Ballistic Computer. The name rangekeeper began to become inadequate to describe the increasingly complicated functions of rangekeeper. The Mk 1 Ballistic Computer was the first rangekeeper that was referred to as a computer. Note the three pistol grips in the foreground. Those fired the ship's guns.
Accurate fire control systems were introduced in the early 20th century. Pictured, a cut-away view of a destroyer. The below deck analog computer is shown in the centre of the drawing and is labelled "Gunnery Calculating Position".
Figure 2 . A conceptual diagram of the flow of fire control data in the Coast Artillery (in 1940). The set forward point of the target was generated by using the plotting board (1). This position was then corrected for factors affecting range and azimuth (2). Finally, fire was adjusted for observations of the actual fall of the shells (3), and new firing data were sent to the guns.