Editing Fire-control system (section)

===World War II===
{{main|Ship gun fire-control system}}

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.<ref name="updates">The degree of updating varied by country. For example, the US Navy used servomechanisms to automatically steer their guns in both azimuth and elevation. The Germans used servomechanisms to steer their guns only in elevation, and the British began to introduce Remote Power Control in elevation and deflection of 4-inch, 4.5-inch and 5.25-inch guns in 1942, according to Naval Weapons of WW2, by Campbell. For example {{HMS|Anson|79|6}}{{'}}s 5.25-inch guns had been upgraded to full RPC in time for her Pacific deployment.</ref> For U.S. Navy gun fire control systems, see [[ship gun fire-control systems]].

The use of director-controlled firing, together with the fire control computer, removed the control of the gun laying from the individual turrets to a central position; although individual gun mounts and multi-gun turrets would retain a local control option for use when battle damage limited director information transfer (these would be simpler versions called "turret tables" in the Royal Navy). Guns could then be fired in planned salvos, with each gun giving a slightly different trajectory. Dispersion of shot caused by differences in individual guns, individual projectiles, powder ignition sequences, and transient distortion of ship structure was undesirably large at typical naval engagement ranges. 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. Gun directors were topmost, and the ends of their optical rangefinders protruded from their sides, giving them a distinctive appearance.

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. Visual range measurement (of both target and shell splashes) was difficult prior to the availability of radar. The British favoured [[coincidence rangefinder]]s while the Germans favoured the [[Stereoscopic rangefinder|stereoscopic type]]. The former were less able to range on an indistinct target but easier on the operator over a long period of use, the latter the reverse.
[[File:FordMk1Rangekeeper.jpg|thumb|right|''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.]]
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. Calculating the proper "lead" given the relative motion of the two vessels was very difficult, and [[Torpedo Data Computer|torpedo data computers]] were added to dramatically improve the speed of these calculations.

In a typical World War II British ship the fire control system connected the individual gun turrets to the director tower (where the sighting instruments were located) and the analogue computer in the heart of the ship. In the director tower, operators trained their telescopes on the target; one telescope measured elevation and the other bearing. Rangefinder telescopes on a separate mounting measured the distance to the target. These measurements were converted by the Fire Control Table into the bearings and elevations for the guns to fire upon. In the turrets, the gunlayers adjusted the elevation of their guns to match an indicator for the elevation transmitted from the Fire Control table—a turret layer did the same for bearing. When the guns were on target they were centrally fired.<ref>B.R. 901/43, ''Handbook of The Admiralty Fire Control Clock Mark I and I*''</ref>

Even with as much mechanization of the process, it still required a large human element; the Transmitting Station (the room that housed the Dreyer table) for HMS ''Hood''{{'}}s main guns housed 27 crew.

Directors were largely unprotected from enemy fire. It was difficult to put much weight of armour so high up on the ship, and even if the armour did stop a shot, the impact alone would likely knock the instruments out of alignment. Sufficient armour to protect from smaller shells and fragments from hits to other parts of the ship was the limit.
[[File:Radar and Electronic Warfare 1939-1945 A28824.jpg|thumb|left|200px|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".]]

The performance of the analog computer was impressive. The battleship {{USS|North Carolina|BB-55|6}} during a 1945 test was able to maintain an accurate firing solution<ref name="caveat">The rangekeeper in this exercise maintained a firing solution that was accurate within a few hundred yards (or meters), which is within the range needed for an effective rocking [[salvo]]. The rocking salvo was used by the US Navy to get the final corrections needed to hit the target.</ref> on a target during a series of high-speed turns.
<ref name="real_case">{{cite journal
 |last         = Jurens
 |first        = W.J.
 |url          = http://www.navweaps.com/index_inro/INRO_BB-Gunnery_p1.htm
 |year         = 1991
 |title        = The Evolution of Battleship Gunnery in the U.S. Navy, 1920–1945
 |journal      = Warship International
 |number       = 3
 |page         = 255
 |access-date  = 2006-10-18
 |archive-url  = https://web.archive.org/web/20061120223502/http://www.navweaps.com/index_inro/INRO_BB-Gunnery_p1.htm
 |archive-date = 2006-11-20
 |url-status     = dead
}}</ref> It is a major advantage for a warship to be able to maneuver while engaging a target.

Night naval engagements at long range became feasible when [[radar]] data could be input to the rangekeeper. The effectiveness of this combination was demonstrated in November 1942 at the [[Naval Battle of Guadalcanal|Third Battle of Savo Island]] when the {{USS|Washington|BB-56|6}} engaged the [[Imperial Japanese Navy|Japanese]] [[battleship]] {{ship|Japanese battleship|Kirishima||2}} at a range of {{convert|8400|yd|km}} at night. '' Kirishima'' was set aflame, suffered a number of explosions, and was scuttled by her crew. She had been hit by at least nine {{convert|16|in|mm|adj=on}} rounds out of 75 fired (12% hit rate).<ref name="early">{{cite journal
  | author = A. Ben Clymer
  | title = The Mechanical Analog Computers of Hannibal Ford and William Newell
  | journal = IEEE Annals of the History of Computing
  | volume = 15 |issue = 2 | pages = 19–34
 |year = 1993
  | url = http://web.mit.edu/STS.035/www/PDFs/Newell.pdf
  | access-date = 2006-08-26
  | doi = 10.1109/85.207741
| s2cid = 6500043
 }}</ref>
The wreck of ''Kirishima'' was discovered in 1992 and showed that the entire bow section of the ship was missing.<ref name="Ballard">{{cite web
| url = http://www.combinedfleet.com/atully08.htm
| title = Located/Surveyed Shipwrecks of the Imperial Japanese Navy
| work = Mysteries/Untold Sagas Of The Imperial Japanese Navy
| access-date = 2006-09-26
| author = Anthony P. Tully
| year = 2003
| publisher =CombinedFleet.com
}}</ref>
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.<ref name="Kirishima">{{cite book
  | last = Mindell
  | first = David
  | title = Between Human and Machine
  | publisher = Johns Hopkins
  | year = 2002
  | location = Baltimore
  | pages = 262–263
  | isbn = 0-8018-8057-2 }}</ref>