Torpedo Director

A British torpedo director, possibly a Pattern 2380 after alteration to a deflection sight.
Images of such devices are incredibly rare.

A Torpedo Director, in British service, is a calculating sight for firing torpedoes, more similar to a settable gunsight than to a gunnery director.

Nature and Function

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The Director Angle is the proper angle between the line of sight to the target and the path of the torpedo. Helping the torpedo officer judge and discern this angle from data available to him by direct observation or external sources is the fundamental purpose of any torpedo director. Additionally, a good torpedo director design should offer its user a quick means of judging whether the target is near enough that the torpedo will be able to reach it.

It should be noted that the proper director angle is dependent upon a proper estimation of enemy heading and speed (expressed in one of several ways), and upon the assumption that his motion while the torpedo is underway will, on average, continue about this mean heading. It is easy to see aiming a torpedo which generally takes longer to reach its target than does a shell requires more cooperation on the part of the target!

The Royal Navy began the 20th century using torpedo directors that modeled the torpedo firing problem according to the Director Triangle — that formed by

1. the path of the torpedo
2. the line of sight to the target at the moment of firing
3. the path of the target between firing and impact.

As the war approached, the Royal Navy refined their hardware along lines they felt were important, issuing improved Marks or adding parts to existing directors.

Small Innovations

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The directors started out pretty basic. Clever torpedomen soon thought of small changes that would make them better, and these were often viewed at the Torpedo School and the best ones standardised for proper fitting and allocation.

• A Radiomir Fore Sight (or just "Radium Fore Sight") is one with a small glass tube containing radium for use in night work. It was often used on Pattern 2380A and the Line of SIght Director. They proved successful, but the luminous substance itself left a desire for looking at alternatives. Other directors had electrical lamps to illuminate their sights.

• A Compass Ring was conceived in 1911 for 2006 and 2391/2392 ... an outer ring marked in Quadrant bearings that could be attached to the base of the director and set to own ship's course. The enemy bar would be clamped to this ring. and it was thought that this ring could be adjusted manually if own ship changed course by reference to a compass near at hand or perhaps by automatic adjustment via a gyrocompass repeater. It sounds like a snafu.

• A Longmore Disc was a disc that showed the inclination of the enemy to the torpedo bar (rather than the sight bar). It was used on the 2380, but in 1915 or thereafter, it was to be replaced by a Robinson Disc.

• A Inclination Disc (or Robinson Disc ) is a disc that rides the sighting arm and is marked 0 to 180 degrees left and right so that target Inclination is directly readable.

• A Gyro Angle Base or "angled stand" was proposed for some directors in 1911 to support the proposed general introduction of torpedoes with angled gyros. It consisted of a pair of discs that could rotate up to 40 degrees either side of zero against each other and lock every 10 degrees (initially) or 5 degrees (from 1916 or so) by use of a conical spring permitted them to be clicked to the same heading a torpedo set to the same gyro angle would take upon being fired.

• A Tangent Bar was a small armature which could be added to a torpedo director to offset its rear sight a short distance to make its sighting angle converge with the track of the torpedo when the director could not be located on or near the firing tube. The idea was an example of the Royal Navy over-thinking the problem, and the service soon great disenchanted with the fragility and complexity they bestowed upon the directors. Some time during the production of directors Pattern 2391a and 2392a, some were being sent out without tangent bars and directors of Pattern 2006 and later that were brought in for repair were sent back without their tangent bars. The conclusion finally reached was that the lateral errors that would remain untreated without the tangent bars were apt to be vastly smaller than the other sources of error inherent in accurate torpedo fire except in very short range attacks. These scenarios were to be treated by choosing a suitably offset aim point on the target.

• A Central Bearing Disc "similar to those fitted in Patts. 2391-2" was considered in 1911 for the 2006 directors.

• A Graduated Sight Bar permitted the user to determine whether the target was presently within range of the torpedo to help eliminate the problem of firing when out of range.

• A Possible Shot Scale was a refinement on the graduated sight bar which allowed the firing range estimation to be resolved without resort to arithmetic.

A Change in Thinking

As the war began, the British were becoming increasingly dissatisfied with their directors, which they regarded as flimsy, mechanically loose, and not very easy or quick to set. Indeed, on the latter point, in 1911 test firings, 6% of torpedoes that missed their target were attributable to errors in setting the director properly or firing the torpedo when out of range. In 1908, the errors made at the director accounted for a full 16% of misses!

Other complaints were more fundamental. The tangent bar was a particular object of disgust, making the director rickety and often being wrongly set in use. More astonishingly, the very value of such a fixture as the tangent bar was finally receiving attention. Why worry about the small lateral errors introduced when the director was not located directly at the torpedo tube when these errors were apt to be tiny in comparison with those caused by the enemy manoeuvring after the torpedo was fired or a failure to accurately judge his speed and heading in the first place?

In 1912 and 1913, the Vernon was recording ideas about Deflection Plotting in such detail that it seems plain that a switch to using deflection as a means of setting the director angles was being actively considered.

In 1915 or so, the Royal Navy was exploring, for the first time, larger questions of torpedo warfare in fleet actions — ones that seem glaringly obvious in hindsight. One aspect of this reconsideration was that the series of torpedo directors they had relied on were to be refashioned to embody the geometry based on the deflection triangle rather than the director triangle.

The deflection triangle is that formed by

1. the path of the torpedo
2. the line of sight
3. a line perpendicular to the line of sight that passed through the point of impact

This last line was equivalent to the target's speed-across if own ship were at rest.

The first step taken was to adapt the existing directors to a deflection aiming, a conversion process that made all above water director become T.D.S. Mark Is, and the line of sight directors T.D.S. Mark IIs. The longer term step was to build torpedo deflection sights optimised to the geometry. These T.D.S. models (Mark III et seq.) would become the late-war successors to the torpedo directors described here.

Royal Navy Torpedo Directors

Pattern 1192/1192a

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These were large, semicircular directors intended for use directing broadside fire. They received some enhancements and alterations, but were considered obsolete by 1912.

Pattern 1193/1193a

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An early director with a 60 degree arc, intended for firing ahead from torpedo craft.

Pattern 1895/1895a

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A lighter version of the 1193, with a 60 degree arc for use in early torpedo craft.

Pattern 2006/2006a

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These compact, circular directors first appeared for use in armoured control towers in 1904-1905, and saw service into the great war.

Pattern 2390/2390a

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A 60 degree director similar to Pattern 1985, available by 1912 at least, supplied to torpedo craft with heater torpedoes.

Pattern 2389/2389a

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Available by 1910 at least, it was similar to the Pattern 2390, but fitted for use from the bridge.

Pattern 2380/2380a

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New in 1914 and similar to the Pattern 2390a, but larger and of improved construction.

Pattern 2387

Available from 1910 at least. Same as Pattern 1192, but fitted for use from the bridge by addition of a tangent bar.

Pattern 2388/2388a

Available by 1910 at least. Same as Pattern 1193, but fitted for use from the bridge by addition of a tangent bar. The 2388a was sturdier and had a solid sight bar, and was probably a 2388 that had been repaired to the new standard, as none of the type was directly manufactured, owing in part to new destroyers not being fitted for fore bridge firing in the 1911 era. By 1916, they were considered obsolete. Like the 1193, they were likely 60 degree arcs.^[Inference]

Pattern 2391/2391a/2392/2392a

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A family of circular directors improving upon the Pattern 2006 introduced from 1909 by adding a sighting telescope and a possible shot scale. In 1912 or so, the -a models appeared which added support for gyro angling.

Pattern 2236

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Entering service in 1915 or 1916, and reflecting the disfavour accorded tangent bars, the 2236 was a modification of the 2391a with the tangent bar and the association telescopic member to offset the sighting telescope removed. It had an inclination disc, a Radiomir fore sight and a deflection bar.

Already in 1916, plans were being drafted to convert these directors into Torpedo Deflection Sights.

Line of Sight Director

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This was a circular director similar to the Pattern 2006, but with a rotating torpedo bar, intended for use on the fore bridge of a light cruiser or smaller vessel.

By mid 1917, following plans drafted in 1916, they were being converted into T.D.S. Mark II (not Mark I, as with all other directors).

Pattern 3340

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This director was intended for use on submarines. On the surface, it would be fitted to the head of the periscope for use on the conning tower. When submerged, it would function as a hand-held calculator to determine the periscope angle to be used for firing.

See Also

• Torpedo Deflection Sight
• Torpedo Deflection Sight Mark I
• Video depicting the principle of a torpedo director