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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.
As is shown in Figure 2, in general, the torpedo does not actually move in a straight path immediately after launch and it does not instantly accelerate to full speed, which are referred to as torpedo ballistic characteristics. The ballistic characteristics are described by three parameters: reach, turning radius, and corrected torpedo speed. Also, the target bearing angle is different from the point of view of the periscope versus the point of view of the torpedo, which is referred to as torpedo tube parallax.<ref name = parallax>{{cite book |editor=Commander Submarine Force, United States Atlantic Fleet |title=Submarine Torpedo Fire Control Manual |orig-year=1950-02 |date=2006-04-16 |url= http://www.maritime.org/doc/attack/index.htm |pages=1–12 |chapter=Definitions |access-date=2006-08-22 |ref=CITEREFCOMSUBATL1950}}</ref> These factors are a significant complication in the calculation of the gyro angle, and the TDC must compensate for their effects.
Straight running torpedoes were usually launched in salvo (i.e. multiple launches in a short period of time)<ref name="spread">{{harvnb|COMSUBATL|1950|loc=§ Definitions pp 1–9}}</ref> or a spread (i.e. multiple launches with slight angle offsets)<ref name="spread"/> to increase the probability of striking the target given the inaccuracies present in the measurement of angles, target range, target speed, torpedo track angle, and torpedo speed.
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====Position keeper====
As with the angle solver, the equations implemented in the position keeper can be found in the Torpedo Data Computer manual.<ref name="tdcv3" /> Similar functions were implemented in the rangekeepers for surface ship-based fire control systems. For a general discussion of the principles behind the position keeper, see [[Rangekeeper]].
==Notes and references==
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