Difference between revisions of "Renouf Torpedo Tactical Instrument"

Revision as of 20:47, 10 March 2011

The Renouf Torpedo Tactical Instrument was a pretty ingenious family of Torpedo Control instruments designed by Lt. Cdr. Edward de Faye Renouf of H.M.S. Conqueror (1911) described in the Annual Report of the Torpedo School, 1917.^[1]

It was proposed in 1917 and foreseen as being delivered in 3 types of increasing complexity and function: A, B and F.

Geometric Theory

Firing at a stationary Target'^[2]

If your target, located at S, is not moving, a torpedo fired from position O will hit him if it is within a circle drawn about S whose radius (OS) equals the maximum range of a torpedo at the given speed setting.

Firing at a moving Target from extreme range'^[3]

If your target, located at S at the moment of firing, is steaming along line AB, a torpedo fired from position O can reach him if it is anywhere within a circle drawn about the impact point, E with a radius equal to the endurance of the torpedo. The limiting range circle, then, will always be centered on the impact point, and distance SE and OE are going to be proportional to the speed of the enemy and the speed of the torpedo, respectively. The centre of the torpedo circle must move in the direction the enemy is steaming by a distance SE, which is equal to the SpeedOfEnemy * MaximumTimeOfFlightOfTorpedo, as both torpedo and target will travel for the same duration between firing and impact.

Firing at a moving Target within range'^[4]

The geometry of the case described above is independent of scale, owing to the similarity of triangles. Consider if we move point O well within the extreme range circle and observe that director angle SOT has the same angles as does SXE (the director angle pertaining to the extreme range case). The enemy inclination would be the same in both cases, as would the director angle required to produce the hit.

Mechanical Design

Type A with bars removed^[5]
Set to show an enemy making 17 knots with baseplate circles for torpedoes reaching: * 18,000 yards at 21 knots * 15,000 yards at 25 knots * 11,000 yards at 29 knots

To save time and space, Renouf instruments typically portrayed several torpedo settings at once by displaying 3 different circles. The scale chosen was 4,000 yards to an inch. The primary structure was formed by a flat base plate with a speed scale for the target ship, adjustable by a knob. The instrument always depicted the target ship steaming left to right across the bottom as indicated by an arrow.

The Base Plate

The red, fixed circle drawn at 10,000 yards from S is meant to suggest the effective range of secondary armament that the attacker might fear. The radial lines drawn every 10 degrees can be read from either of two scales to treat them as:

• enemy inclinations in attacking problems, or those where the enemy is the ship depicted at S
• relative bearings to the enemy for defensive calculations where we consider our own ship to be at S.

This somewhat schematic diagram shows how each of 3 link gears (suggested in gold here) might advance its respective torpedo range circle a different distance along AB according to the different times of flight for the different torpedo speeds as enemy speed is dialed in. Thus, in this implementation, point S is always in the middle of the lower edge of the instrument, and the circles are advanced different distances, displacing their centers (the impact points) rightward toward B. The torpedo rings are painted in white at portions where firing would be unwise owing to:

• low striking angle of torpedo against hull
• low relative speed (when firing from astern)
• ease of evasion, as the enemy is nearly combing the wake already
• deleterious effect of enemy course estimation errors^{[Citation needed][6]}

This is similar to how the Renouf instruments effected this, but even the simplest Mark added no fewer than 4 bars to depict various tactical considerations.

The Position Bar

Type A^[7]
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."

A Type for Attack

This type, illustrated above, was the simplest. It was intended for use in cruisers, light cruisers, flotilla leaders, and destroyers. Its emphasis was delivering a torpedo attack.^[8]

It could determine:^[9]

• 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

Can the attacker 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

What is 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.

How 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.

[TO BE CONTINUED - TONE]

B Type for Battleships

This type was fancier than the "A" and intended for use aboard battleships and battlecruisers. The emphasis here was primarily defensive, but could also be used for attack calculations if torpedo circles of one's own torpedoes were substituted for those of the enemy.^[10]

In addition to the capabilities of the "A Type", the "B" could answer the following defensive questions as pertained to one's own ship:^[11]

• are we within range of enemy torpedoes?
• if so, what course change is sufficient to cause them to fall short?
• what is the track angle of the enemy's torpedo, in case I want to comb the wakes?
• how long until his torpedo crosses my track?

F Type for Flagships

This was for use in flagships, and was the most complex model, as it was oriented toward torpedo attack and defence not at the ship level, but the level of a division, a squadron, or even three squadrons. It could also help identify, from the perspective of the fleet being considered, safe and unsafe arcs for one's own torpedo fire.^[12]

History and Deployment

Unknown [TO BE CONTINUED - TONE]

See Also

Footnotes

Bibliography