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</ref><ref name=OtherTrackers>While the TDC's target tracking abilities were unique for submarine torpedo fire control during WWII, target tracking was used on surface ship torpedo fire control systems by a number of nations (see references in this article to [http://www.maritime.org/doc/destroyer/ddfc/index.htm US destroyer] and [http://www.fischer-tropsch.org/primary_documents/gvt_reports/USNAVY/USNTMJ%20Reports/USNTMJ-200F-0086-0124%20Report%20O-32.pdf Japanese torpedo fire control] {{Webarchive|url=https://web.archive.org/web/20070720142332/http://www.fischer-tropsch.org/primary_documents/gvt_reports/USNAVY/USNTMJ%20Reports/USNTMJ-200F-0086-0124%20Report%20O-32.pdf |date=2007-07-20 }}). The TDC was the first analog computer to miniaturize the capability enough for deployment on a submarine.</ref>
Replacing the previously standard hand-held [[slide rule]]-type devices (known as the "banjo"
The TDC was a rather bulky addition to the sub's [[conning tower]] and required two extra crewmen: one as an expert in its maintenance, the other as its actual operator. Despite these drawbacks, the use of the TDC was an important factor in the successful [[commerce raiding]] program conducted by American submarines during the [[Pacific war|Pacific]] campaign of World War II. Accounts of the American submarine campaign in the Pacific often cite the use of TDC.<ref name=clear>{{cite book | last = O'Kane | first = Richard | title = Clear The Bridge:The War Patrols of the U.S.S. Tang | publisher = Bantam Books | year = 1977 | ___location = New York | isbn= 0-553-14516-9 |ref=harv}}</ref><ref name=wahoo>{{cite book | last = O'Kane | first = Richard | title = Wahoo: The Patrols of America's Most Famous World War II Submarine | publisher = Bantam Books | year = 1987 | ___location = New York | isbn= 0-553-28161-5}}; Beach, Edward L., Jr., Captain, USN (rtd). ''Run Silent, Run Deep'', ''passim''; Beach, ''Dust on the Sea'', ''passim''; Grider, George. ''War Fish'', ''passim''; Blair, Clay, Jr. ''Silent Victory'' (New York: Bantam, 1976), ''passim''.</ref> Some officers became highly skilled in its use,<ref>[[Robert Edson Dornin|Dusty Dornin]] was widely agreed to be the best. Blair, p.357.</ref> and the Navy set up a training school for its use.<ref>Blair, p.357.</ref>
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===History===
The problem of aiming a [[torpedo]] has occupied military engineers since [[Robert Whitehead]] developed the modern torpedo in the 1860s. These early torpedoes ran at a preset depth on a straight course (consequently they are frequently referred to as "straight runners"). This was the state of the art in torpedo guidance until the development of the [[homing torpedo]] during the latter part of [[World War II]].<ref name=othertorps>There were other forms of torpedo guidance attempted throughout WWII. Notable are the Japanese human-guided ''[[Kaiten]]'' and German [[G7e#G7e/T3|pattern running]] and [[acoustic homing]] types for attacking convoys. Today, most submarine-launched torpedoes are wire-guided with terminal homing.</ref> The vast majority of submarine torpedoes during World War II were straight running, and these continued in use for many years after World War II.<ref name=USMk14his>{{cite web|url = http://www.geocities.com/Pentagon/1592/ustorp5.htm|title= Part Five: Post WW-II Submarine Launched/ Heavyweight Torpedoes|accessdate=2006-07-26|author= Frederick J Milford|date= October 1997|work= US Navy Torpedoes|archiveurl=https://web.archive.org/web/20060523064716/http://www.geocities.com/Pentagon/1592/ustorp5.htm|archivedate=2006-05-23}}</ref> In fact, two World War II-era straight running torpedoes — fired by the British nuclear-powered submarine {{HMS|Conqueror|S48|6}} — sank the [[ARA General Belgrano|ARA ''General Belgrano'']] in 1982.
During [[World War I]], computing a target intercept course for a torpedo was a manual process where the fire control party was aided by various [[slide rule]]s<ref name=fleetsub>{{cite web | title = Torpedo Data Computer | work = FleetSubmarine.com | year = 2002 | url = http://www.maritime.org/tdc.htm | accessdate = 2006-07-03 }}</ref> (the U.S. examples were the [[Mark VIII Angle Solver]] (colloquially called the "banjo", for its shape), and the "Is/Was" circular sliderule ([[Nasmith Director]]), for predicting where a target will be based on where it is now and was)<ref>Holwitt, Joel I. ''"Execute Against Japan"'', Ph.D. dissertation, Ohio State University, 2005, p.147; Beach, Edward L., Jr. ''Run Silent, Run Deep''.</ref> or mechanical calculator/sights.<ref name = dread>{{cite web |title = Firing a Torpedo Using A Mechanical Computing Sight |work=The Dreadnought Project |url =http://www.dreadnoughtproject.org/tfs/index.php/Torpedo_Director|year=2000
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A straight-running torpedo has a [[gyroscope]]-based control system that ensures that the torpedo will run a straight course.<ref name="straight">Straight after an initial turn to course, as explained below.</ref> The torpedo can run on a course different from that of the submarine by adjusting a parameter called the gyro angle, which sets the course of the torpedo relative to the course of the submarine (see Figure 2). The primary role of the TDC is to determine the gyro angle setting required to ensure that the torpedo will strike the target.
Determining the gyro angle required the real-time solution of a complex [[Trigonometry|trigonometric]] equation (see [[Torpedo Data Computer#math 1|Equation 1]] for a simplified example). The TDC provided a continuous solution to this equation using data updates from the submarine's navigation sensors and the TDC's target tracker. The TDC was also able to automatically update all torpedo gyro angle settings simultaneously with a fire control solution, which improved the accuracy over systems that required manual updating of the torpedo's course.<ref name=AutomatedGyroSetting>{{harvnb|Friedman|1995|p=196}}</ref>
The TDC enables the submarine to launch the torpedo on a course different from that of the submarine, which is important tactically. Otherwise the submarine would need to be pointed at the projected intercept point in order to launch a torpedo.<ref name="GyroPointing">Torpedoes were developed by the United States with this capability during WWI. However, without automated fire control it was difficult to realize the full advantages of this approach.</ref> Requiring the entire vessel to be pointed in order to launch a torpedo would be time consuming, require precise submarine course control, and would needlessly complicate the torpedo firing process. The TDC with target tracking gives the submarine the ability to maneuver independently of the required target intercept course for the torpedo.
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