Handbook for Fire Control Instruments

1914

Repository	Document ID	Pages	Dimensions	Plates
TNA	ADM 186/191	72	20cm x 33cm	113

This manual appears quite valuable for learning about the transmitting and receiving devices for relaying orders between action stations. My copy is a black and white photocopy.

CONTENTS.

LIST OF PLATES.

NOTES

The primary focus of this handbook is the data transmitters and receivers that conveyed commands, indications, and range and deflection data between the various stations of a ship.

Chapter I

This chapter outlines the organization of the gun groups, transmittering stations, control positions, spotting tops, and the like in the various ships of the fleet.  Instruments could be characterized as being step-by-step or as being direct working.  Step-by-step instruments had a number of discrete indications they could signal, typically on odometer-like revolving drums seen through windows, and the nature of the device required that each possible reading be worked through one by one until the desired status was conveyed.  Direction working instruments did not have to index through the settings, and hence were faster but required more wires in their umbilicus.

Instruments used by the RN were produced by Barr and Stroud, Vickers (both of the step-by-step type), and Siemens (direct working), as well as some fire gongs from Graham & Company.

Chapter II --  Siemens' Instruments

Siemens Mark I. Instruments

The Siemens Mark I. family of instruments were early examples of direct-working equipment.  Their utility in 1914 appears limited, as the range of indications they permit (maximum range 9975 yards) was insufficient for tactical demands of the coming war.  Cross-referencing with Appendix I, it appears that the only ships fitted with Siemens' Mark I. gear at the time this handbook was created were Albion, Goliath, Ocean, Vengeance, and Canopus.

	Pattern No.
Siemens Mark I. Range Transmitter	90
Siemens Mark I. Range Receiver	86
Siemens Mark I. Deflection Transmitter	88
Siemens Mark I. Deflection Receiver	84
Siemens Mark I. Order Transmitter	89
Siemens Mark I. Order Receiver	85

 

The Siemens Mark I. Range Transmitter (Pattern No. 90) was apparently an old system, capable of sending ranges from 0 to 9,975 yards.  It had 3 handles on it, each able to indicate a figure on a quadrant underneath.  Inside, drums would rotate to establish the proper connections to energize wires needed to replicate the indicated figure on the receiver.  Drums A and B had 10 positions (0-9) to convey thousands and hundreds of yards, and drum C having 4 positions to convey 00, 25, 50 or 75.  Consequently, the reading could not be read across, but your eye would have to see which number was being pointed at in each of the 3 positions.  The levers had a small push-button on their tips which presumably had to be depressed before the lever could be moved to another position, and which locked it precisely in one of the positions when released.

The Siemens Mark I. Range Receiver (Pattern No. 86) was the corresponding device to remotely indicate a range transmitted by the Mark I. Transmitter.  It also had 3 drums to indicate the range, each with a star-like ring of electromagnets (10 in A and B, 4 in C).  The 28 wires connecting the transmitter to the receiver would cause the 3 drums in the receiver to spin to indicate the range commanded at the transmitter, as it energized the proper electromagnet within the drum, causing it to spin to allow this particular magnet to face one on the housing.  Presumably, the range was read off a line of windows permitting the labelled faces of the 3 drums to be read.  I do not know if the housing was rectangular or had a rounded front face or top edge.

The Siemens Mark I. Deflection Transmitter and Receiver (Pattern Nos. 88 and 84) were minor adaptations of the Pattern 90 and Pattern 86.  The sole difference was that the rightmost (C) drums had "Right" and "Left" written on it rather than 00, 25, 50 or 75.  I do not know whether there were 2 or 4 positions for the transmitter's rightmost lever.  One would imagine they'd have tweaked it to have just 2 positions.  By Royal Navy practice, then, the Mark I. deflection gear could indicate 99 knots left or right deflection as a maximum, which was an ample domain.

The Siemens Mark I. Order Transmitter (Pattern No. 89) allowed the relay of firing orders by the position of a clock-like indicating hand.  There were three positions it could assume -- the one at the 12 o'clock position was labelled "CEASE", the one at 4 o'clock was "CONTROL", and at 8 o'clock "INDEPENt" with the T curiously shrunk to connote the abbreviation of "independent".

The Siemens Mark I. Order Receiver (Pattern No. 85) had a small window through which "Control'd". "Cease" and "Independent" (from top to bottom) could be read on the swinging sector visible through it.  Apparently, a loss of power at the device would cause "Cease" to be the setting indicated, as the other two positions are obtained by magnetic influence overpowering a centering spring device.  The device needed 2 wires for its electromagnets (coming from its transmitter) and a single wire for its return.

Siemens Mark II. Instruments

The Mark II. family of devices were refinements of the earlier generation.  Appendix I indicates that only Glory was equipped with them.  The drums in the Mark II. instruments employed 5 magnets instead of the 10 used in Mark I., and this allowed fewer wires (15 + 2 power leads of larger diameter) to be used to tie transmitter to receiver.  The full range of 10 indicating positions for the drums A and B was retained by clever combinations of electromagnets being employed rather than the use of a single magnet for each position as in the Mark I. devices.

	Pattern No.
Siemens Mark II. Range Transmitter	96
Siemens Mark II. Range Receiver	93
Siemens Mark II. Deflection Transmitter	94
Siemens Mark II. Deflection Receiver	91
Siemens Mark II. Order Transmitter	95
Siemens Mark II. Order Receiver	92
Siemens Mark II. Rate Transmitter	-
Siemens Mark II. Rate Receiver	-

There was also a Siemens Mark II. Rate Transmitter and Receiver pair (no Pattern Nos. assigned, apparently) which bore close resemblance to the Range instruments, but with an 4th element and handle.  Drums A, B and C had 10 positions and communicated values from 0 to 99.9 in tenths.  The fourth handle had 3 positions:  "Open", "Close" and a blank spot showing when no rate should be taken from the indicator.  It required the 17 wires of the Mark II. range instruments plsu an additional 2 wires for the fourth element.  I have to confess I have no idea what units this dynamic range of +/- 99.9 was meant to employ.

Chapter III -- Vickers Dial Instruments

Vickers dial instruments were step-by-step devices.  The range and deflection transmitters had tell-tale receivers built into them to indicate the value, and a single handle by which to drive the value through its range.

There was no separate order instruments, but a 3 position "check fire switch" could be set to "Control Fire" versus "Check Fire", and the receivers would indicate its setting by exposing a red or a white disc, respectively.  The intermediate position of this switch was labelled "Off" and removed power from the attached instruments entirely. 

The receivers were either combined types which received range, deflection and orders, or a simple deflection receiver.

	Pattern No.
Range transmitter with 1:1 gearing	103
Range transmitter with 4:1 gearing and 1/4 inch figures	319
Deflection transmitter with 1:1 gearing	102
Deflection transmitter with 4:1 gearing and 1/4 inch figures	318
Check fire switch	101
Combined receivers	99
Combined receivers with 1/2 inch figures	320
Single deflection receiver	317

The size of the figures on the various devices is not always specified in the text.

The range and deflection instruments were similar.  The range receivers had 4 cyclometer drums (meaning the complete revolution of a drum caused the one to its left to shift one position) enabling the display of ranges up to 19,975 yards.  As in the Siemens instruments (and in keeping with RN practice), the rightmost drum had only four readings for 00, 25, 50 and 75.  The leftmost drum, then, had only a 0 position (for ranges up to 9,975 yards) and a 1 position to add 10,000 yards to the range otherwise indicated.  The deflection receivers had 2 independent pairs of drums on the same shaft, each pair capable of counting up to 50, with one being for Left deflection and the other for Right deflection.  A pair of shutters are arranged such that when the Left counters reach zero knots, the Left counters are covered by their shutter and the shutter that had been covering the Right counters flips up to reveal their reading, and vice-versa.

An electric motor or magnetic armature drove the receiver drums.  Stops built into the design prevented the counter dials from spinning past their limits of indication but did not hamper the spinning of the motor.  This, then, became the mechanism employed to bring the tell-tale at the transmitter and the receiver into synchronization -- the person working the transmitter would simply drive the tell-tale's reading to the maximum limit then to its minimum limit, and this action would square all receivers with it if they had been out of step previously.

There was also an adaptation to the devices for synchronization to avoid the delays involved in the recovery procedure outlined above:  the check fire switch would be set to "Off", a butterfly nut would be removed from a threaded hole on th side of the receiver, and a long spindly "key" could be inserted.  Some manner of twisting of this key could set the dials as needed, and then the key would be withdrawn and the butterfly nut would be replaced.

The range transmitter's handle for setting the range was originally geared so that a quarter revolution of the handle changed the range by 25 yards.  This was soon altered by the addition of gearing to make a full turn of the handle equate to 25 yards range or a single knot of deflection.

 

Chapter IV -- Vickers Follow-the-Pointer Instruments

Follow-the-pointer (F.P.) systems were an important advance over the digital systems described above where range and deflection data was indicated by receivers in numeric form.  A sightsetter with a sight equipped with F.P. receivers for range and deflection had only to work his handles to keep the indicating pointers whose positions were influenced by the transmitted values in line with an indicating pointer on the sight.  His action in so doing would impart the range and deflection onto the sight in an eye-hand coordination task of the simplest and most natural description.  In contrast, the earlier equipment forced the sightsetter to look at numbers and then find them on a circular dial, and spin them to a pointer.  This method required much more thought and it was impossible to see in an instant whether the requested settings had been applied.

The range dials on gunsights, however, had range graduations that were not uniformly spaced.  This meant that while the tell-tale receiver located at the transmitter could have regular markings around its dial face, the motor on the F.P. receiver on the gunsight needed mechanical help to map this regular range scalar into the distorted relationship between range and dial angles on the gunsight.

	Mark I.	Mark II.		Mark III.	Mark III.*
	4-inch Guns	6-inch Guns	4-inch Guns
Range transmitter	2,643	2,647	2,651	2,660	2,690
Range receiver	2,645	2,648	2,652	2,662	-
Range repeat receiver	-	-	-	2,662	-
Deflection transmitter	2,644	2,649	2,653	2,661	2,691
Deflection receiver	2,646	2,650	2,654	2,679	-
Deflection repeat receiver	-	-	-	2,679	-
Mark III. receivers are complete electrical portion on base plate only.  The complete receivers and repeat receivers have different pattern numbers for each type of gun.

 

Vickers Mark I. F.P. Instruments

The transmitter's handle had a grip-switch which functioned to interrupt the electrical contacts inside when the handle was not being gripped and rotated.  Not much more detail is offered.

Vickers Mark II. F.P. Instruments

One revolution of the range transmitter handle causes the range pointer to rotate 15 arc minutes.  How many yards of range this equates to would be dependent on the range strip in use.  One revolution of the deflection transmitter handle equates to 1.5 knots of deflection.

Vickers Mark III. F.P. Instruments

No real data is offered, but a simple explanation of F.P. operation is for some reason located in this section.  By the absence of any reference to this system in the 1909 handbook, we can infer that the Mark III. F.P. systems were not on the scene until at least 1910.

Vickers Mark III.* and Mark IV.* F.P. Instruments

These were mechanical transmitters that could be employed as master transmitters to drive 2 or more transmitters in a unified manner.  Gears and shafts connected the motion of the transmitting handle to 2 or more regular transmitters located nearby (typically, mounted on a bulkhead when the geared shafts lying against the bulkhead as well).  The Mark IV.* is noted as being a minor improvement, and that it is being fitted in the Queen Elizabeth class.

Plate 10 depicts these mechanical transmitters installed and driving multiple range transmitters.  The design features corrector boxes near each subordinate transmitter which apparently afford the opportunity to apply small offsets to the various transmitters to cause them to deviate from the mechanical input.  I think this is finally the explanation I have long lacked as to how salvo spreads in range were effected, though it would only seem to work when the guns were in local laying mode.  By the absence of any reference to them in the 1909 handbook, we can infer that these systems were not on the scene until at least 1910.

Vickers F.P. Range Clock

A special variant of the range clock had a F.P. III. transmitter switch.  Its receivers had equal-spaced range dial divisions for full charge firing, and Usborne pointer accelerating gear was used on the receiver for reduced charge and other modes of fire, as these dials had unequal range spacings.  The transmitter was revolved by hand to keep a following pointer in line with that pointer driven by the range clock, and this action relayed the range to the receivers.  This was the range transmitter for the latest 6-inch guns being produced.  The range repeat receivers had equal spacings, just like the clock.

Usborne Pointer Accelerating Gear

Cam elevated sights had equal range spacings for their full charge firing, as it was this ballistic problem for which the cam was devised.  When the gun was to be worked with reduced charges or aiming rifles, the range spacings had to be unequal to deal with the vastly different nature of the ballistics.  The Usborne equipment was designed to "tweak" the pointer angles received by the proper amount to account for this altered spacing on the range dial.

When switching to these alternate firings from normal full charge, the receiver dial had to be changed, the full charge pointer removed, and the Usborne accelerating equipment then mounted on the gun.  The transmitter and its repeat were not altered. 

The Usborne gear connected to the receiver spindle, but converted its action so that rather than having the spindle directly drive the receiver pointer as in the case of full charge firing the spindle's rotation drove a cam assembly to convert its pointer angles to those required by the range dial being used.  A combination of grooves on the cam plate allowed the operator to select between sub-caliber or reduced charge or the use of two aiming rifles.

The 6-inch guns in the Iron Duke, Royal Sovereign and Queen Elizabeth classes and Tiger used this.

Chapter V -- Barr and Stroud Instruments

Barr and Stroud instruments in use at the time this handbook was written were of the Mark II., II.*, and III. types except for some of the ships first fitted which had Mark I. gear.  By comparing this to the 1909 handbook, we can tell that the Mark III. equipment was introduced some time after 1909.

	Mark
	I.	II.	II*.	III.	III*.	IV.
Combined range deflection and order receiver	-	78	2,596	3,141	-	-
Transmitter	-	80	2,597	3,140	-	-
Single range receiver	-	2,592	2,598	3,142	-	-
Single range transmitter	-	2,593	2,599	3,132	-	-
Single order receiver	53	-	2,600	2,604	-	-
Single order transmitter	57	-	2,601	2,605	3,133	-
Rate receiver	811	2,594	-	2,960	3,135	-
Rate transmitter	812	2,595	-	2,961	3,134	-
Bearing receiver	2,590	-	2,602	2,606	-	3,139
Bearing transmitter	2,591	-	2,603	2,607	-	3,138

Barr and Stroud Mark I. Order Transmitter

The upper portion of the case had three apertures through which the indications could be read.  The indications were on vulcanite sleeves on spindles which protruded out the sides of the case where handles permitted them to be rotated through 90 degrees or so to the desired command (each had just two positions).  A spring pin within the transmitter grabbed the spindle to secure it within either of the two of the positions.  Moving a handle to the down position completed the corresponding circuit to the receiver.

Each sleeve's face was marked with either two command indications or a command and a blank face, and the reverse side contained contacts that would complete a circuit in one position and break it in the other.  When the handles were in their down position, the corresponding order circuit was energized, and they were otherwise off. 

By inference from the remarks for the Mark I. Order Receiver, I think the 3 channels functioned in the following fashion, top to bottom.

Lever/Shutter Up (off)	Lever/Shutter Down (on)	Notes
Cease	blank	It is possible that the transmitter read "Open" when down
blank	Indep	It is possible that the transmitter read "Controlled" when up
blank	Fire	A single-stroke gong atop the receiver sounds when transitioning from off to on.

 

Barr and Stroud Mark I. Order Receiver

The receiver resembled the transmitter, minus the handles.  The three windows showed 3 fixed shutters underneath.  The top shutter has the word "Cease" on it, and the lower two are blank.  Each window additionally has a spring-loaded armature fitted which can, by the action of an electromagnet, swing another shutter in front of this fixed shutter with the result that the articulated shutter's labels are then visible. The swinging shutters are labelled, top to bottom, as blank, "Indep." and "Fire".

A single-stroke gong is fitted to the top of the receiver, and the circuit is such that the gong sounds a single time when the lower shutter switches from its blank state to "Fire".  In this manner, the operator of the transmitter sounds firing gongs at the receivers when he moves the lowest handle to the "Fire" position.  The receiver requires four wires to control its 3 separate shutters and provide a return.

Barr and Stroud Mark II. Combined Range Deflection and Order Transmitter

This transmitter placed deflection at the top, orders in the middle, and range in the bottom position.  Each had a handle on the right side of the instrument for setting the desired value.  The available orders were displayed in a list on the front such that all were continually visible, and a pointer moved by the order handle would move it up or down to the order desired.  This design helped the operator understand which direction of handle motion would yield motion toward the desired command.  A Mark II combined receiver would be placed nearby to indicate the values of all inputs.  In this way, the orders were somewhat redundantly indicated.

Though the image I have for Plate 21 is not very clear, I'd say the order list looks as follows: SALVO COMM, INDEP COMM, then 6 indecipherable slots (possibly blank), CHECK FIRE, CEASE FIRE.  If the intervening slots are indeed blank, I would imagine that this was to permit future additions while in the meantime creating an ample number of steps between those settings which command fire and those which command a cessation!  The pointer to indicate the selected command was a pair of fingers which would frame the selected command.  This mechanical tell-tale prevented the order transmitter from rolling cyclically.

The deflection handle was geared so one revolution of the handle registered 1 knot, the order handle needed half a revolution to change to the next order, and the range handle had a clever double-geared design to allow fast or slow changes to be made.  Ordinarily, a single revolution of the handle yielded a change of 25 yards, but when the handle was pressed in and spun, this quadrupled to 100 yards per spin. 

The provision of the high speed gearing modification for the range data might be a nod to the weakness in step-by-step systems that large changes in reading could take time to apply.  It is worth noting that even with this gearing in place, the average synchronization operation where the transmitter was driven to one limit and then the other would take 250 revolutions of the handle!

None of the range and deflection transmitters in the Barr and Stroud family had stops, but the drums in the receivers did.  The order transmitter did have a hard stop at each end of the series, owing to the linear nature of the mechanical tell-tale incorporated into the design.

Barr and Stroud Mark II. Combined Range, Deflection and Order Receiver

Curiously, the position of the indicators on the receiver (orders at the top, then deflection, then range) does not match those used in the transmitter.  The rightmost drum for range in this case had 8 positions, with each value (00, 25, 50, 75) occurring twice.  The drums, and their readings, were visible through aperatures on the front of the case.

Barr and Stroud Mark II. Single Range Transmitter and Receiver

These were used in ships fitted with Vickers deflection instruments and in later ships for allowing transmitting stations and control positions to communicate.

The instruments looked as though both transmitter and receiver as though the corresponding parts of the combined type had been prized out and packaged separately.

Barr and Stroud Mark II.* Instruments

These were outwardly indistinguishable from the Mark II. family, but their internal wiring and brushes differed.  The function would have been identical, and the changes were perhaps to enhance problems maintaining connectivity in Mark II, plugs-- the most common type of failure particular to that series.

Barr and Stroud Mark III. Instruments

With the sole exception of the Single Range Receiver, the Mark III. instruments differed from their Mark II. and Mark II.* equivalents only in their wiring interface.  Whereas the Mark II. housings each required 2 or 3 individual cables to enter, the Mark III. devices each consolidated their wiring to receive just a single multi-core cable through a gland.   I presume that the outward appearance and function was otherwise identical to the earlier instruments.  The Single Range Receiver, however, had other features to improve its function as a reporter of discrete range estimates sent down from a rangefinder.  As there is no mention of these in the 1909 handbook, we can infer that these were all introduced in 1910 or later.

Barr and Stroud Mark III. Single Range Receiver

This range receiver had a shutter which normally obscured the indicated range.  A "range cut" button at the rangefinder could be depressed to energize a coil which would flip the shutter aside to reveal the range reading.  The shutter remains in a catch until such time as the transmitter changes the range it is signalling.  A lever on the left of the receiver could be used to lock the shutter in the open position if desired.  This feature rendered unnecessary the use of a separate buzzer circuit which was apparently used with earlier instruments.

A twisted knob on the right side of the receiver could apply a differential range in increments of 25 yards up to a maximum of 1000 yards up or down.  The intent here was to permit rangefinders to be "biased" into agreement or to account for differences between their location and that of the gun platform being directed.

This instrument had 2 apertures rather than just one.  The second one indicated the correction reading being applied.

Barr and Stroud Mark I. Bearing Transmitter and Receiver

The Mark I. model allowed the digital relay of a bearing 0 to 893/4 in 1/4 degree increments along with a compass quadrant read on 2 separate swinging shutters (when the coils for the shutters are energized, the shutter is lowered), one to the left of the degrees and one to the right.  For instance, the display might read N 401/2 E.  If the shutter coils are unenergized, the compass quadrant would read S.W.  When both are energized, the shutters would raise to read N.E.

There is one handle for the numeric reading on the lower right side of the transmitter, and another for setting the quadrant on the front of the housing below the drums and apertures.  A complete turn of the degree handle sets a change of one degree in the bearing indicated.  I am not sure of the gearing on the compass quadrant setting handle.

Barr and Stroud Mark II.* Bearing Transmitter and Receiver

These were similar to the Mark I. instruments, but worked in relative bearings, not compass bearings.  An additional digit drum was fitted to permit angles of 0 to 180 in 1/4 degree increments, and a single remaining shutter located underneath the digital bearing drums could be in either STARBOARD or PORT position (starboard was in the higher position, and so would be visible when the shutter was lowered).  I guess that this shutter was also in the raised position when the coil was off.

One small difference was that the transmitter handle had to be pushed in before would engage the drums inside.  A spring would keep it out, otherwise.  The degree handle was on the right side near the bottom, and the shutter setting handle on the left near the bottom.  I am not sure if the degree drums and the shutter position were intertied, or what behavior would result if the angle was driven to (or past) its maximum reading.

Similar to the Mark I. instruments, the transmitter had an integral tell-tale for angle and port/starboard. The Mark II.* Rate of Change transmitter was fundamentally similar, with CLOSING and OPENING on the shutter.

Barr and Stroud Mark III. Bearing Transmitter and Receiver

These were similar to the Mark II.* instruments in that they communicated a relative bearing angle in quarter degree increments, but a second shutter was added which was blank on the high position and marked "TRAIN" in the lower space.  This shutter, then, could emphasize that the indicated bearing was not just a declarative but an imperative -- the mount was to train to match the indicated angle.

The arrangement placed the new shutter at the top of the housing, with the STARBOARD/PORT shutter below it and the degree readout at the bottom.  Beneath all indicators was the switching rotors and handles.  The right side had a large degree-setting handle (again with a spring-loaded design as in the Mark II.* design), and the left side had two smaller handles for setting the position of the shutters.

Again, the transmitter had the tell-tale integrated into its housing, and the receiver appeared like a shorter transmitter (lower gearbox and handles omitted).

Barr and Stroud Mark IV. Bearing Transmitter and Receiver

This is identical to the Mark II.* model, but the STARBOARD/PORT shutter has a third face added to the bottom, which is blank.  It has no blank/TRAIN shutter. I do not understand why this would be considered an improvement unless the digit display can go all the way up to 360 (or down to -180), and this was intended to be used with the blank face of the shutter on display.  The receiver was the same, minus the handles and lower gearbox.

Barr and Stroud Mark I. Rate of Change Transmitter and Receiver

Two concentrice drums, as in the Mark II. deflection instruments (??), allowed range rates to be communicated.  The outer drum reads "Open" or "Close" and the inner drum's digits represent the number of seconds taken to open or close 50 yards, and are seen through apertures in the outer drum.  This method of conveying a range rate is highly unusual compared to the later standarized practice of measuring range rate in yards per minute, but John Brooks indicates that this was an earlier system for tracking changes in range, often accomplished by use of a stopwatch, though one can imagine this would get frantic indeed at rates of closure exceeding 300 yards per minute.  Apparently, the Mark I Dumaresq had its range rates marked off on its dial plate in this manner.

From the plates, I cannot say I fully understand the display except noting that the reading was taken through a single aperture in the front of the housing.. 

Barr and Stroud Mark II. Rate of Change Transmitter and Receiver

These are identical to the Mark II* bearing instruments except for the marking on the drums.  They could count a range rate by 10s from 0 to 1990 (presumably, in yards per minute), with the words INCREASING or DECREASING being on the shutter below the digital display.  Some of these instruments were later modified to match the Mark II.* design described below. Cables entered the enclosure by 2 glands at the bottom edge.

Barr and Stroud Mark II.* Rate of Change Transmitter and Receiver

This minor adaptation on the Mark II. design replaced the two rightmost digit drums with the standard 00, 25, 50, 75 drum.  The shutter below the digits was also reworded to read OPEN or CLOSE.  It's puzzling that the Mark II did not meet the standard Royal Navy terminology or its protocol of measuring range rates in 25 yard per minute granularity.

Barr and Stroud Mark III. Rate of Change Transmitter and Receiver

Mostly as the Mark II.* design, but the shutter has a third position which would be blank, and the other faces have been reworded again to OPENING and CLOSING. 

Barr and Stroud Mark III.* Rate of Change Transmitter and Receiver

As Mark III., but all cables entering the housing now used a single gland.

Barr and Stroud Mark IV. Rate of Change Transmitter

Same as Mark III. except the shutter coils and digital drums are fed their input from without and not directly from the transmitter and shutter switches.  This allowed the tell-tale indicators to receive their data from a change-over switch, as though they were an ordinary receiver.  This removed the need for a COS to have its own tell-tale indicator in cases where it was going t o be placed adjacent to the transmitter anyway.

Barr and Stroud Mark III. Order Instruments

These were similar to the order component of the combined transmitter, with the indicator of the orders on the front face.  Like the other model, it, too had space for 10 orders.  No indication in the handbook reveals what the orders were.  If you recall, the combined instrument seemed to have only 4 of its 10 command slots utilised.  The front face of the transmitter was somewhat redundant, as it had the list of commands with the present on pointed to by an indicator on a rack and pinion and yet the lower portion of the enclosure had a receiver element whose drum provided a mechanical tell-tale of the same selection.   The mechanical tell-tale prevented the transmitter from rolling cyclically.

Barr and Stroud Mark III.* Order Transmitter

This was like the Mark III. type, but had a single cable gland rather than 2.  The mechanical tell-tale prevented the transmitter from rolling cyclically past its end.

Chapter VI. -- Evershed's Bearing Indicators

These instruments permitted equipment in control positions (telescopes and periscopes) to transmit their relative angle of bearing to distant stations.  The transmitters could be adapted to many devices, and some receivers could themselves transmit should conditions require a station ordinarily controlled by an aloft observer (e.g.: a turret) to itself become the source of bearing data informing other turrets or the transmitting station.  Like so many of the devices of the day, the transmitters and receivers communicated in steps, with a degree being the angular increment.

The forward transmitting station was equipped with a selector switch (similar to the C.O.S.) which allowed any receiver on board to be connected to any transmitter.  All Evershed systems were fed their power through the transmitting station, which in turn fed off of a generator (called the "isolator") or its back-up unit.

The absence of any reference to Evershed equipment in the 1909 handbook indicates that it appeared in 1910 or later.  Other sources have implied that it was still being deployed at the beginning of the war.

Evershed Bearing Transmitters

Transmitters were of Type 1 or 2.  Type 2 transmitters were adapted to receive as well as transmit (and so featured an indicator), but Type 1 transmitted only.  Each transmitter was equipped with a control key which could be thrown off to signal receivers when the operator wished to relinquish control (e.g.: if the target could no longer be seen from that station). 

Most ships carried a pair of gunsight telescopes on pedestals equipped with Type 1 or Type 2 transmitters, one for port and the other for starboard targets.  A change-over switch at the top permitted the one that can better bear on the target to be selected, presumably to transmit down a single set of cables.

The conning and director towers each had a a periscope on the centerline (or one on port and one on starboard) with crosswires and Type 1 or Type 2 transmitters and 5x magnification. Those with paired transmitters again employed a C.O.S. to select the one to transmit.

The gun control tower usually had a Type 2 (adapted to receive as well as transmit) under the rangefinder mounting.  It transmitted the bearing of the rangefinder.

Some transmitters were freely dirigible in training and elevation whereas others employed gearing and handwheels within a given arc of control.  The crosshairs could be illuminated just as any sighting telescope.  You'll note, however, that if director tower were attached to the transmitter, deflection and drift angles might mean that it did not directly face the target whose bearing should be indicated.  To allow this deviation to be factored out, transmitters could be fitted with special means of entering drift and deflection.

Evershed Bearing Receivers

Receivers were similarly Type 1 or Type 2, again with Type 2 connoting a bi-directional capability governed by a control key.  The turret handing rooms would be equipped with receivers of either type which would read the turret's bearing by tracking the turret training rack.  Turrets equipped with Type 2 receivers would have the control key in the center sighting position for use by the trainer.

Evershed Bearing Indicators

Type 1 indicators (or "gun-sight indicators") were placed near a turret trainer's scope so he could look through its eyepiece with his left eye while his right eye was using the sighting periscope. The left gun in a turret would have this indicator on its right sight.  The indicator was viewed through an eyepiece much like the sighting scope, and the operator would see a needle on a small galvanometer scale to indicate whether he was on in training or off to left or right.  A rheostat knob permitted the illumination of the device to be adjusted, but the light would be turned off when the turret was not under control, and this would render the needle and the gauge invisible.

The manner of reading the needle and the gauge is that when the needle was to the left side (say), the mounting needed to be traversed to the left to obtain the correct bearing.  When the pointer was properly positioned in the center of the scale, the training was correct within the granularity of the transmitter (that is, one degree... not all that precise!)

Type 2 indicators (or "open-faced indicators") were general purpose instruments for general use.  All turrets mounted both types of indicator.  Transmitting positions that had to receive (i.e.: those with Type 2 Transmitters) employed the open-faced Type 2 indicator to display the data, else they had no indicator.  The officer's position in gun turrets featured a Type 2 indicator so the officer could monitor the trainer's correct performance.

Type 2 looked like the Type 1 did (galvanometer needle on a scale), but were plain dials easily monitored without need for peeking in an eyepiece.  Rather than lighting on/off to indicate control. and flag visible through an aperture would indicate "ON" or "OFF".

Control Keys

These were sometimes part of the transmitter proper (or Type 2 receiver), and sometimes mounted separately.  When in the on position, gunsight indicators are lit and open-face indicators show "ON" to indicate control (and vice-versa).  The control key had a small galvanometer needle which would indicate how many stations were receiving its output when turned on.

Evershed Selector Switch

The selector switch was actually a gunmetal panel with an array of rotary switches on it residing in the transmitting station.  Each switch represented a different receiving station (a station containing a receiver of either type, or a Type 2 transmitter), and each position for the switches represented a numbered control position capable of transmitting bearing data (from a transmitter of either type or a Type 2 receiver).

For example, the King George V's selector switch is depicted in Plate 38.  It has 7 switches for 7 receiving stations (one for each of 5 turrets, Conning Tower, and Control Tower), and each switch has up to 4 positions in addition to an "off" state which would deny it any input.  The 4 control stations specified are B Turret, Control Tower, Conning Tower, and X Turret (1-4, respectively).  Blank positions on the switches corresponding to the stations capable of transmitting as well as receiving effectively prevent a control station from driving its own receivers.

The switch could permit all stations to monitor bearing data from a given control station or to form groups of receiving stations monitoring separate control stations.  When a control station was being monitored by 1 or more receiving stations, it was common practice to set its own receiving station switch to "OFF", but it was possible to have this control station in turn monitor the bearings generated by a second control station.  This would permit the first control station to generate bearing data as usual, but also allow it to mimic the bearing of the second should it lose sight of the object being tracked, presumably by slewing their device to the indicated bearing.