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| - These warship-based computing devices needed to be sophisticated because the problem of calculating gun angles in a naval engagement is very complex. In a naval engagement, both the ship firing the gun and the target are moving with respect to each other. In addition, the ship firing its gun is not a stable platform because ships roll, pitch, and yaw due to wave action, ship change of direction, and effect of board firing. The rangekeeper also performed the required ballistics calculations associated with firing a gun. This article will focus on US Navy shipboard rangekeepers, but the basic principles of operation are applicable to all rangekeepers regardless of where they are deployed.
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| abstract
| - These warship-based computing devices needed to be sophisticated because the problem of calculating gun angles in a naval engagement is very complex. In a naval engagement, both the ship firing the gun and the target are moving with respect to each other. In addition, the ship firing its gun is not a stable platform because ships roll, pitch, and yaw due to wave action, ship change of direction, and effect of board firing. The rangekeeper also performed the required ballistics calculations associated with firing a gun. This article will focus on US Navy shipboard rangekeepers, but the basic principles of operation are applicable to all rangekeepers regardless of where they are deployed. A rangekeeper is defined as an analog fire control system that performed three functions:
* Target tracking The rangekeeper continuously computed the current target bearing. This is a difficult task because both the target and the ship firing (generally referred to as "own ship") are moving. This requires knowing the target's range, course, and speed accurately. It also requires accurately knowing the own ship's course and speed.
* Target position prediction When a gun is fired, it takes time for the projectile to arrive at the target. The rangekeeper must predict where the target will be at the time of projectile arrival. This is the point at which the guns are aimed.
* Gunfire correction Directing the fire of a long-range weapon to deliver a projectile to a specific location requires many calculations. The projectile point of impact is a function of many variables, including: gun azimuth, gun elevation, wind speed and direction, air resistance, gravity, latitude, gun/sight parallax, barrel wear, powder load, and projectile type. During WWII, all the major warring powers developed rangekeepers to different levels. Rangekeepers were only one member of a class of electromechanical computers used for fire control during World War II. Related analog computing hardware used by the United States included:
* Norden bombsight US bombers used the Norden bombsight, which used similar technology to the rangekeeper for predicting bomb impact points.
* Torpedo Data Computer (TDC) US submarines used the TDC to compute torpedo launch angles. This device also had a rangekeeping function that was referred to as "position keeping." This was the only submarine-based fire control computer during World War II that performed target tracking. Because space within a submarine hull is limited, the TDC designers overcame significant packaging challenges in order to mount the TDC within the allocated volume.
* M-9/SCR-584 Anti-Aircraft System This equipment was used to direct air defense artillery. It made a particularly good account of itself against the V-1 flying bombs. During World War II, rangekeeper capabilities were expanded to the point where the name rangekeeper was deemed to be inadequate. The name computer, which had been reserved for human calculators, then began to be applied to the rangekeeper equipment. After World War II, digital computers began to replace rangekeepers. However, components of the analog rangekeeper system continued in service with the US Navy until the 1990s. The performance of these analog computers was impressive. The battleship USS North Carolina during a 1945 test was able to maintain an accurate firing solution on a target during a series of high-speed turns. 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 Third Battle of Savo Island when the USS Washington engaged the Japanese battlecruiser Kirishima at a range of at night. The Kirishima was set aflame, suffered a number of explosions, and was scuttled by her crew. She had been hit by nine rounds out of 75 fired (12% hit rate). The wreck of the Kirishima was discovered in 1992 and showed that the entire bow section of the ship was missing. 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. Even the British did not adopt gyroscopic stabilization of their guns until quite late in the history of rangekeepers. Rangekeepers were very large, and the ship designs needed to make provisions to accommodate them. For example, the Ford Mk 1A Computer weighed The Mk. 1/1A's mechanism support plates, some an inch (25 mm) thick, were made of aluminum alloy, but nevertheless, the computer is very heavy. On at least one refloated museum ship, the destroyer USS Cassin Young (now in Boston), the computer and Stable Element more than likely still are below decks, because they are so difficult to remove. The rangekeepers also required a large number of electrical signal cables for synchro data transmission links over which they received information from the various sensors (e.g. gun director, Pitometer, rangefinder, gyrocompass) and sent commands to the guns.
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