Renouf Torpedo Tactical Instrument Type A

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The Type A ("A" standing for "Attack") was the simplest of a family of Renouf Torpedo Tactical Instruments, intended for use in cruisers, light cruisers, flotilla leaders, and destroyers.

Its emphasis was to help plan the approach for a torpedo attack.[1]

Mechanical Design

The Type A used 4 separate bars to depict various tactical considerations.

The Position Bar

Type A[2]
Set to show an attacker making 26 knots, intent on firing from 11,000 yards and 45 degrees off the bow of a target at a present range of 20,000 yards and making 17 knots with circles for torpedoes reaching: * 18,000 yards at 21 knots * 15,000 yards at 25 knots * 11,000 yards at 29 knots

The Position Bar (shown in orange) was pivoted at point S and scaled along its length in thousands of yards. It would be swung to the proper angle to indicate the target's inclination (in attack mode) or the threat's relative bearing (in defence mode). A slider along the scale would be positioned to estimated range, and this bore a pivot point (referenced below). A disc about the hub at S would be referenced later, with the Course to Steer bar, and a small switch (shown in green) would indicate whether the attack from coming from port or starboard (as the instrument always depicts an attack from port).

The Desired Track Bar

The Desired Track Bar (shown in pink and pivoted from the position pointer on the position bar) depicted the proposed movement of the attacker to reach his preferred firing position. It pivoted from the position pointer and was graduated in "DISTANT TO RUN IN THOUSANDS OF YARDS" from the position pointer. A sliding Desired Position Pointer on this bar could be slid to a position to indicate the position the attacker would like to attain. The orientation of this bar and the placement of its pointer, then, would indicate a proposed firing position on the base plate relative to S.

The "Course to Steer" Bar

The "Course to Steer" Bar' (depicted in blue) pivoted around S and was graduated in knots on the same scale used on the target speed scale. A pointer near its hub indicated on the graduated disc at the base of the position bar. This would indicate the relative bearing the attacker would have to place the target to achieve the desired attack position indicated by the desired position pointer.

The Resultant Track Bar

The 'Resultant Track Bar (depicted in pink on the left) was on a pivot that was free to slide along the target's speed scale. It was graduated in "time in minutes to run 1,000 yards along the desired track bar."

Functionality

Folding Table[3]

The instrument could determine:[4]

  • whether torpedo fire was possible from the present position
  • when fire was possible, which torpedo setting would be most advantageous
  • how to steer to attain a specific desired firing position
  • how long it would take to attain that firing position
  • the deflection setting for the torpedo deflection sight

Determine whether you can fire a torpedo now

This could be worked out as follows:

  1. place the position bar to the inclination (or bearing, if you are the target) of the enemy
  2. slide the position pointer to the present range
  3. set the estimated enemy speed by the knob (this would advance the torpedo circles)
  4. the attacker is able to fire using any torpedo setting if the position pointer falls within its torpedo circle

Determine the best setting for the torpedo

Generally, this was held to be the fastest setting, or the smallest circle the position pointer falls within, subject to inviolable orders for torpedo settings or other vital tactical considerations (such as wanting the torpedo to over-run).

If, however, one wanted to allow for the enemy turning away, one could examine which setting would suffer least from it by rotating the position bar anti-clockwise by an amount equal to the turn away expected. This represents the situation if the turn were made now, and so the smallest circle from this new inclination would represent the best choice.

Determine course to steer to achieve attack position

This could be worked out as follows:

  1. place the position bar to the inclination of the target
  2. slide the position pointer to the present range to the target
  3. set the estimated enemy speed by the knob (this would advance the torpedo circles)
  4. position the desired track arm and its desired position pointer
  5. position the resultant track bar to the speed of the target and make it parallel to the desired track bar
  6. rotate the "course to steer" bar so that attacker's speed is indicated on the resultant track bar
  7. the pointer on the course to steer bar will indicate the relative bearing the target should be placed on to achieve the desired attack position

Consider the configuration of the instrument in the illustration above. It is set up to work an attack problem where

  • initial range 20,00 yards
  • initial estimated inclination 100 degrees right
  • initial estimated enemy speed 17 knots
  • desired attack position 11,000 yards at an inclination (bearing?) of 135 degrees right
  • our speed is 26 knots

This will require a run of 13,000 yards with the enemy bearing 70 degrees red. A time to run 1,000 yards along desired track is about 2 minutes, so time to attain our desired position is about 26 minutes.

Type A Example 2[5]

In another example, Example 2 shows an attacker making 25 knots, intent on firing from 13,000 yards and inclination 135 right of a target at a present range of 25,000 yards and inclination 170 degrees right and making 18 knots. The instrument shows that the attacker will have to run 17,000 yards after bringing the enemy to bearing green 50. As the time to run 1,000 yards will take about 45 seconds, the attacker will have to cruise for a little under 13 minutes before it will achieve the attack position.

Determine how long will it take to achieve attack position

When the "Course to Steer" bar is swung to meet the resultant track bar at the attacker's speed, a triangle of velocities is formed in which the length of the resultant track is the movement of the attacker during his approach to firing. It is graduated in time to run 1,000 yards along the resultant track. The distance to be made along the desired track can be read from the position of the desired position pointer and then multiplied by the figure indicated on the resultant track bar to obtain the total time required before the attack can be made.

Determine the deflection setting for the sight

Renouf Instrument Deflection Sliderule[6]

A slide rule was fitted to the side of all Renouf instruments to allow the torpedo sight deflection (the target speed-across if attacker were at rest, or TargetSpeed times sin(Inclination)). The slide in this rule (marked at inclination angles, 0 to 90) had an arrow at its 90 degree mark which would be positioned to indicate the enemy speed. When this was done, the target inclination on the slider would be opposite the knots of deflection on the fixed speed scale, which was graduated from 1 to 32 knots.

History and Deployment

These were apparently only allocated after the war. In 1919, five were to be manufactured by Elliott Brothers and allocated to these vessels in this order: Castor, Wallace, Spenser, Campbell, Delhi.[7]

See Also

Footnotes

  1. Annual Report of the Torpedo School, 1918. p. 180.
  2. Annual Report of the Torpedo School, 1918. Plate 123.
  3. Annual Report of the Torpedo School, 1919. Plate 54.
  4. Annual Report of the Torpedo School, 1918. p. 181.
  5. Annual Report of the Torpedo School, 1918. Plate 124.
  6. Annual Report of the Torpedo School, 1918. p. 184, Fig VII.
  7. Annual Report of the Torpedo School, 1919. p. 118.

Bibliography

  • H.M.S. Vernon. Annual Report of the Torpedo School, 1917. Originally C.B. 1474. Copy 7 at The National Archives. ADM 189/37.
  • H.M.S. Vernon. Annual Report of the Torpedo School, 1918. C.B. 1527. Copy 20 at The National Archives. ADM 189/38.