TORPEDO DATA COMPUTER

The Torpedo Data Computer (TDC) turned into an early electromechanical analog laptop used for torpedo fire-control on American submarines at some stage in World War II. Britain, Germany, and Japan additionally evolved automated torpedo fireplace control device, however none had been as advanced as the US Navy's TDC, as it became capable of automatically track the goal as opposed to simply supplying an instantaneous firing answer. This particular functionality of the TDC set the same old for submarine torpedo hearth manipulate throughout World War II.

Replacing the formerly wellknown handheld slide rule-kind devices (referred to as the "banjo" and "is/became"), the TDC become designed to provide hearth-manage solutions for submarine torpedo firing in opposition to ships walking at the surface (floor warships used a special laptop).

The TDC changed into a as a substitute bulky addition to the sub's conning tower and required  greater crewmen: one as an professional in its renovation, the alternative as its actual operator. Despite these drawbacks, using the TDC become an important component within the a hit trade raiding software performed by way of American submarines during the Pacific campaign of World War II. Accounts of the American submarine marketing campaign within the Pacific frequently cite using TDC.Some officers have become especially skilled in its use, and the Navy set up a training college for its use.

Two upgraded World War II-technology U.S. Navy fleet submarines (USS Tusk and Cutlass) with their TDCs maintain to serve with Taiwan's navy and U.S. Nautical Museum team of workers are assisting them with keeping their device.[10] The museum additionally has a totally restored and functioning TDC from USS Pampanito, docked in San Francisco. The hassle of aiming a torpedo has occupied navy engineers since Robert Whitehead evolved the cutting-edge torpedo inside the 1860s. These early torpedoes ran at a preset intensity on a instantly direction (consequently they're regularly called "straight runners"). This changed into the kingdom of the artwork in torpedo guidance till the development of the homing torpedo for the duration of the latter a part of World War II. The vast majority of submarine torpedoes throughout World War II had been directly jogging, and those persisted in use for decades after World War II. In reality,  World War II-technology instantly jogging torpedoes — fired with the aid of the British nuclear-powered submarine HMS Conqueror — sank the ARA General Belgrano in 1982.

During World War I, computing a goal intercept course for a torpedo was a manual process wherein the hearth control birthday celebration was aided by means of various slide policies (the U.S. Examples were the Mark VIII Angle Solver (colloquially known as the "banjo", for its shape), and the "Is/Was" circular sliderule (Nasmith Director), for predicting in which a target can be based on wherein it's far now and become) or mechanical calculator/sights. These were often "woefully faulty", which helps provide an explanation for why torpedo spreads had been recommended.

During World War II, Germany, Japan, and america each developed analog computers to automate the technique of computing the desired torpedo course.
In 1932, the Bureau of Ordnance (BuOrd) initiated improvement of the TDC with Arma Corporation and Ford Instruments. This culminated in the "very complicated" Mark 1 in 1938. This turned into retrofitted into older boats, starting with Dolphin and up thru the most modern Salmons.

The first submarine designed to apply the TDC changed into Tambor, launched in 1940 with the Mark III, positioned inside the conning tower. (This differed from earlier outfits.) It proved to be the quality torpedo fire control machine of World War II.

In 1943, the Torpedo Data Computer Mark IV become advanced to support the Mark 18 torpedo.

Both the Mk III and Mk IV TDC had been evolved via Arma Corporation (now American Bosch Arma).

 

 illustration of general torpedo fire-control problem

A instantly-going for walks torpedo has a gyroscope-primarily based manage gadget that ensures that the torpedo will run a straight direction. The torpedo can run on a route different from that of the submarine by way of adjusting a parameter called the gyro angle, which units the route of the torpedo relative to the course of the submarine . The primary position of the TDC is to decide the gyro angle putting required to make sure that the torpedo will strike the goal.

Determining the gyro attitude required the real-time answer of a complicated trigonometric equation (see Equation 1 for a simplified instance). The TDC furnished a non-stop approach to this equation using records updates from the submarine's navigation sensors and the TDC's goal tracker. The TDC become also capable of robotically replace all torpedo gyro angle settings concurrently with a fireplace manipulate answer, which progressed the accuracy over structures that required manual updating of the torpedo's direction.

The TDC allows the submarine to release the torpedo on a path distinct from that of the submarine, that's essential tactically. Otherwise the submarine might need to be pointed at the projected intercept point so one can release a torpedo. Requiring the complete vessel to be pointed for you to release a torpedo could be time eating, require particular submarine direction control, and might needlessly complicate the torpedo firing process. The TDC with goal monitoring offers the submarine the potential to move independently of the required goal intercept course for the torpedo.

As is shown in Figure 2, in general, the torpedo does now not definitely move in a directly route without delay after release and it does no longer instantly accelerate to complete velocity, which might be referred to as torpedo ballistic traits. The ballistic characteristics are described by using three parameters: attain, turning radius, and corrected torpedo velocity. Also, the target bearing perspective isn't the same as the factor of view of the periscope versus the factor of view of the torpedo, that's known as torpedo tube parallax. These elements are a enormous hassle in the calculation of the gyro attitude and the TDC have to make amends for their results.

Straight jogging torpedoes were normally launched in salvo (i.E. A couple of launches in a short period of time) or a spread (i.E. More than one launches with mild angle offsets) to boom the chance of striking the goal given the inaccuracies gift inside the size of angles, target range, target velocity, torpedo track perspective, and torpedo velocity.

Salvos and spreads have been additionally launched to strike difficult targets a couple of instances to make certain their destruction. The TDC supported the firing of torpedo salvos by using allowing brief time offsets between firings and torpedo spreads by means of adding small perspective offsets to every torpedo's gyro perspective. Before the sinking of South Korea's ROKS Cheonan by North Korea in 2010, the ultimate warship sunk via a submarine torpedo assault, the ARA General Belgrano in 1982, was struck through two torpedoes from a 3 torpedo unfold.

 

 A look inside the TDC showing the motor drive the position keeper.

 To as it should be compute the gyro angle for a torpedo in a wellknown engagement scenario, the target path, speed, range, and bearing must be appropriately known. During World War II, target path, variety, and bearing estimates frequently needed to be generated using periscope observations, which have been incredibly subjective and mistakes susceptible. The TDC become used to refine the estimates of the target's path, range, and bearing via a manner of

*  Estimating the target's path, speed, and variety based totally on observations.

*  The use of the TDC to are expecting the goal's function at a destiny time based totally on the estimates of the goal's direction, pace, and variety.

* Comparing the anticipated position towards the actual position and correcting the envisioned parameters as required to achieve settlement among the predictions and commentary. Agreement between prediction and observation way that the target course, speed, and variety estimates are accurate

 Estimating the target's course become typically taken into consideration the maximum hard of the remark obligations. The accuracy of the result was fantastically depending on the experience of the skipper. During fight, the real course of the goal changed into not generally decided however as an alternative the skippers determined a related amount called "perspective on the bow." Angle on the bow is the attitude shaped by way of the goal path and the road of sight to the submarine. Some skippers, like Richard O'Kane, practiced determining the attitude on the bow by means of searching at IJN ship models set up on a calibrated lazy Susan via an inverted binocular barrel.

To generate target role facts as opposed to time, the TDC needed to resolve the equations of movement for the goal relative to the submarine. The equations of motion are differential equations and the TDC used mechanical integrators to generate its answer.

The TDC needed to be placed close to different fireplace manipulate device to minimize the amount of electromechanical interconnect. Because submarine area in the pressure hull was restricted, the TDC needed to be as small as possible. On World War II submarines, the TDC and other fire control equipment turned into installed within the conning tower, which was a very small space. The packaging trouble changed into severe and the performance of a few early torpedo hearth manage equipment turned into hampered by means of the want to make it small. It had an array of handcranks, dials, and switches for facts input and display. To generate a hearth manipulate answer, it required inputs on

 *Submarine route and pace, which have been examine mechanically from the submarine's gyrocompass and pitometer log
 * envisioned target path, pace, and variety facts (obtained using data from the submarine's periscope, Target Bearing Transmitter (TBT), radar, and sonar)

 * torpedo kind and velocity (kind was had to deal with the unique torpedo ballistics)

 The TDC accomplished the trigonometric calculations required to compute a goal intercept route for the torpedo. It also had an electromechanical interface to the torpedoes, permitting it to routinely set publications whilst torpedoes had been nevertheless in their tubes, geared up to be fired.

The TDC's goal monitoring functionality turned into used by the hearth manage birthday party to continuously update the hearth manipulate solution even at the same time as the submarine turned into maneuvering. The TDC's goal monitoring potential also allowed the submarine to appropriately hearth torpedoes even when the target become briefly obscured by means of smoke or fog.

 TDC Function Despriction 

Since the TDC actually completed two separate functions, generating target position estimates and computing torpedo firing angles, the TDC simply consisted of two types of analog computers:

*Angle solver: This laptop calculates the desired gyro perspective. The TDC had separate attitude solvers for the forward and aft torpedo tubes.
*Position keeper: This pc generates a continuously up to date estimate of the target function based on earlier goal function measurements.

Angle Solver

The equations carried out inside the angle solver can be discovered within the Torpedo Data Computer manual. The Submarine Torpedo Fire Control Manual discusses the calculations in a standard sense and a significantly abbreviated form of that dialogue is offered here.

The wellknown torpedo fireplace control trouble is illustrated . The trouble is made extra tractable if we expect: 

  * The periscope is on the line shaped by means of the torpedo walking alongside its direction
  * The target actions on a set course and velocity
  * The torpedo moves on a fixed direction and velocity 

 These assumptions are not true in widespread because of the torpedo ballistic traits and torpedo tube parallax. Providing the info as to the way to accurate the torpedo gyro angle calculation for ballistics and parallax is complex and past the scope of this text. Most discussions of gyro perspective willpower take the easier method , that's called the torpedo fire manage triangle. Figure 3 offers an correct version for computing the gyro attitude when the gyro perspective is small, commonly much less than 30°.

The results of parallax and ballistics are minimum for small gyro angle launches because the course deviations they cause are commonly small sufficient to be ignorable. U.S. Submarines at some stage in World War II preferred to fire their torpedoes at small gyro angles because the TDC's fireplace manipulate answers were most accurate for small angles.
The trouble of computing the gyro attitude setting is a trigonometry trouble that is simplified by means of first considering the calculation of the deflection attitude, which ignores torpedo ballistics and parallax. For small gyro angles, θGyro ≈ θBearing − θDeflection. A direct application of the regulation of sines to Figure 3 produces Equation 1.

 

where

   VTarget is the speed of the target.
    VTorpedo is the velocity of the torpedo.
    θBow is the perspective of the target deliver bow relative to the periscope line of sight.
    θDeflection is the angle of the torpedo path relative to the periscope line of sight.

 Range plays no function in Equation 1, which is genuine as long as the three assumptions are met. In fact, Equation 1 is the identical equation solved with the aid of the mechanical sights of steerable torpedo tubes used on floor ships in the course of World War I and World War II. Torpedo launches from steerable torpedo tubes meet the three stated assumptions properly. However, an correct torpedo release from a submarine requires parallax and torpedo ballistic corrections when gyro angles are massive. These corrections require understanding variety appropriately. When the target range turned into no longer known, torpedo launches requiring big gyro angles had been no longer encouraged.[45]

Equation 1 is regularly modified to replacement track attitude for deflection attitude (song angle is described in Figure 2, θTrack=θBow+θDeflection). This change is illustrated with Equation 2.

 

 Wherein θTrack is the perspective among the goal ship's direction and the torpedo's route.
Figure four: Deflection attitude versus tune angle and target pace (θGyro = 0°).

A range of publications country the foremost torpedo tune angle as one hundred ten° for a Mk 14 (46 knot weapon). Figure four indicates a plot of the deflection perspective as opposed to music angle when the gyro angle is 0° (i.E.., θDeflection=θBearing). Optimum music angle is described because the point of minimum deflection perspective sensitivity to music attitude mistakes for a given goal velocity. This minimal occurs on the points of zero slope on the curves in Figure 4 (those factors are marked by way of small triangles).

The curves show the solutions of Equation 2 for deflection angle as a function of goal speed and track attitude. Figure 4 confirms that 110° is the premiere track attitude for a 16-knot (30 km/h) goal, which could be a not unusual deliver speed.

Position keeper

 

As with the perspective solver the equations carried out within the angle solver can be discovered in the Torpedo Data Computer manual.[40] Similar features have been implemented inside the rangekeepers for floor ship-based totally hearth manage structures. For a preferred discussion of the principles behind the placement keeper, see Rangekeeper.