Torpedo Director

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

As the war began, the British were becoming increasingly dissatisfied with their directors and were exploring, for the first time, larger questions of torpedo warfare in fleet actions. One aspect of this reconsideration was that the series of torpedo directors they had relied on were to be refashioned to embody the deflection triangle rather than the director triangle and to thereafter be superceded by a sturdier sight designed for that geometric model — the Torpedo Deflection Sight.

Nature and Function

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 &mdash 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.

As an example, parts such as the Tangent Bar were conceived to allow the small lateral errors created when the sight was not located directly at the torpedo tube to be painstakingly factored out. These were later found to compromise an already loose framework while ignoring the fact that these errors were apt to be tiny in comparison with those caused by the enemy maneuvring after the torpedo was fired or a failure to accurately judge his speed and heading in the first place.

Combining their view that the directors were flimsy, mechanically loose, and not very easy or quick to set..

More fundamentally, however, by 1915 the British were convinced that the director triangle was not the best means of establishing the proper director angle for firing and started to migrate toward a different geometric model called the Deflection Triangle — 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. The longer term step was to built Torpedo Deflection Sights optimised to the geometry. These would become the late-war successors to the torpedo directors described here.

Small Innovations

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 is one with a small glass tube containing radium for use in night work.

• 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.

Royal Navy Torpedo Directors

Pattern 1192/1192a

A large, semicircular director, presumably of the director triangle principle, not used in any modern ships as of 1912. If a 1192a existed, it was similar, but made stronger in its pivots and sighting bar. As of 1916, it was noted as being in use in the H.M.S. Pelorus class, and its semicircular nature related to its employment as a "broadside director". Some were fitted with tangent bars and regraduated to 2/3rd scale for use from TBD fore bridges and heater torpedoes.

Pattern 1193/1193a

Graduated sighting bar for range determination, pp 47-48 Sight is 1193 (as it has sight bar graduations)

Had a 60 degree arc, used in early torpedo craft. If a 1193a existed, it was similar, but made stronger in its pivots and sighting bar. Likely available in 1903, with a graduated sighting arm. It was sometimes called the "Right Ahead" director.

Pattern 1895/1895a

Very similar to the 1193, the 1895 had a 60 degree arc and was used in early torpedo craft. If a 1895a existed, it was similar, but made stronger in its pivots and sighting bar. It lacked graduations on its sighting arm. In 1909, those used with heater torpedoes had their scales regraduated at 2/3rds scale to allow for the faster torpedoes.

Pattern 2006/2006a

Thirty of these compact, circular directors were ordered for trial at 'Vernon and at sea in 1904. Its torpedo arm was not pivoted, and the square knob for the enemy speed pinion was geared such that each flat of the square knob was a knot of enemy speed (4 knots per turn). The sights were fine wires in sighting arches. The distance from the fore sight to the pivot of the sight bar was fixed at 17 inches.

Probably ready for service some time in 1905m it was used in conning towers and director towers of "earlier ships" (as judged by 1912) with a tangent bar, and perhaps also at times directly on tubes. The 2006a was fitted for adapting to gyro angles, sometime after 1912.

The directors had slides underneath permitting some lateral motion (3 inches?) to look around obstacles.

In 1912, a design was approved to add a central bearing disc and a Carpenter's disc sight to the director.

By 1916, displeasure with tangent bars was such that Pattern 2006 directors and later brought in for repair were sent back without their tangent bars.

Pattern 2380/2380a

Similar to the Pattern 2390a, but larger and of improved construction. By 1916 (at least), it had a possible shot scale and inclination disc. It was a 50 degree sector model designed especially for light cruisers. The enemy bar pivot was much stronger than on the 2390a. A lettered disc provided on the 2380 to set enemy heading in relation to the torpedo bar was obsolete by or before 1916. The 2380a differed by having the lettered disc removed in favor of an inclination disc and a Radiomir fore sight.

By mid 1917, these were being altered to the deflection model.

Pattern 2389/2389a

Available by 1910 at least. Same as the Pattern 2390, but fitted for use from the bridge, presumably by the addition of a tangent bar. It almost certainly was a circular design.^[Inference]

Pattern 2390/2390a

Disc added to 2390 to help set course of enemy as expressed as inclination.
Note the lack of any graduations on the sighting arm.

Available by 1912 at least, supplied to torpedo craft with heater torpedoes. Similar to Pattern 1895, but graduated for higher torpedo and enemy speeds. It was not circular, and probably a 60 degree arc like the 1895.^[Inference] It lacked graduations on its sighting arm, but by 1916 at least, they sported inclination discs. The 2390a had more rigid pivots, sturdier construction, and a sighting arm that was solid rather than slotted, and made of hard rolled brass.

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. By 1916, they were considered obsolete. They may have been semi-circular.^[Inference]

Pattern 2391/2391a/2392/2392a

A Pattern 2391 director similar to the 2392. The 2392 would differ by having its telescope mounted to the left of the sighting bar. The possible shot scale depicted is graduated for a Mark VI* heater torpedo (35 knots to 4,000 yards)

Additional maximum firing range scales for use on Pattern 2391/2391a,2392/2392a directors using different tupes of torpedoes.

A "right handed" director for use in conning and director towers of ships from at least 1909-1910. They had open sights as well as the capability to mount a telescope. The 2391a was fitted for gyro angling, sometime after 1912.

In 1912, a design was approved to add a Carpenter's disc sight to the director.

These were circular directors modified from the 2006.

The telescopes used initially had crosswires, a 5-power magnification, and field of view of 7 degs, 10 minutes. It was not given illumination, as the regular sights would be used at night. Improvements in moving the rear sight along the tangent bar were incorporated, and an additional scale along the sighting bar allowed the maximum firing range to be read off directly. A disc labelled 0 to 180 degrees, port and starboard was added and a pointer on the speed and course of enemy bar. This disc was fitted only when a director was mounted on its ship, as the disc was oriented to own ship's keel, with 0 degrees being forward. The intent was that enemy heading could be communicated and set on the sight as a relative heading to own ship's course.

The original telescope in use was a Pattern 2393 of 5 power and field 7 degrees 10 minutes, but in 1915, the need for the lower power scope for haze and rain was realised. A quick trial resulted in the Pattern 3341 of 2.5 power, ~25 degree field being introduced, likely sometime in 1916.

Around 1910, as on the 2006, the directors were provided slides underneath permitting 3 inches of lateral motion to look around obstacles.

By mid 1917, the 2391a and 2392a models were being altered to deflection method.

Pattern 2236

Entering service in 1915 or 1916, and reflecting the disfavor 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.

Line of Sight Director

This was a circular director similar to the Pattern 2006 intended for use on the fore bridge of a light cruiser or smaller vessel. It sat on fixed circular base marked in relative bearings 0 to 180 degrees and the torpedo arm could pivot to match any torpedo training being used aft.^{[Citation needed]}

By mid 1917, they were being adapted to the deflection model.

Royal Navy Submarine Torpedo Directors

Handbook of Torpedo Control plate V, VI: Pattern 3340

See Also

• Torpedo Deflection Sight