Turret Control Table
The Turret Control Table, Pattern 6880, was a compact range-only Dreyer Fire Control Table intended for use should a turret have to resort to local control using only its roof-mounted rangefinder.
Following a May 1912 request to propose a Dreyer table for local control, Dreyer worked with Elliotts to develop a design from August. A solid proposal was in hand around October, 1913. This range-only table was mounted to the rear bulkhead of the turret to conserve space where it could plot data from the turret's rangefinder and to take over if the connection to the TS were to break down for any reason.
The device as first proposed included a Mark IV (or "turret") dumaresq which tracked the training angle of the turret, a range clock to drive a clock range pencil on the range plot, an automatic plotter to display cuts triggered from the RF, and a spotting corrector to convert clock range to gun range.
One was available for trial in Queen Mary's 'B' turret by 27 March 1914, which is slightly unusual, as there is no clear indication that her longer-surviving sisters were ever provided these.
The system described in a hand-typed document from 1913 has some features omitted from that design documented in the 1918 Dreyer table handbook, though some may merely be beyond the scope of the second document.
It featured an automatic range transmitting mechanism which could place its gun range, plus all corrections, directly on the sights. The device was to use commutators in lieu of manual F.T.P. for sending its indications on to the sights. Three cams would be provided for full charge, reduced charge and sub-caliber firing, which is an unusual choice, as the gunsights have such cams as well. Possibly, this could be explained if those cams were not entirely uniform in scale. A handle (a mechanical switch?) is mentioned, which might mean these cams did not have to be swapped out, but were all in the housing.
The 1913 design was to have an integral dumaresq, and a second, remotely mounted one for reference of the Officer of Quarters. His device would provide him a handle by which he can alter the range rate in use on the table's own dumaresq and range clock.
It was also to feature a time-of-flight corrector (controlled by range and rate — seemingly a pared-down Dreyer Calculator) which would automatically inject its correction to the range being transmitted, and have an integral spotting corrector and a remote by which the OOQ can apply his own corrections.
Mechanical handles to ring fire gongs for left and right guns were to be near the OOQ.
A COS would permit the turret to choose between ranges coming from this table or those being sent from the TS.
It is unclear whether any tables were delivered in the form described in 1913. The 1918 design is documented in a much more terse, but much more convincing form, and is generally simpler. The cloned dumaresqs and spotting correctors were eradicated, with the integral devices being removed. The automatic transmission of ranges was also stricken, as was the time-of-flight corrector.
Just as the large Dreyer tables, the Turret Control Table was powered by an electric motor (20 volts provided by a turbo generator in the turret) with a hand-crank governed by a stopwatch being available should power fail.
An adapted, remotely mounted Mark IV dumaresq was connected by flexible shafting to the turret training ring, and thereby kept the fore-and-aft bar aligned with own ship's keel. In this way, and line of bearing was always that of the turret's present training angle. Except for deflection, this was the correct setting for the dumaresq. The indicated range rate on this dumaresq arrived at the table and set the rate on its integral range clock. The table's integral dumaresq described in the 1913 document had disappeared.
The range clock's familiar variable speed drive (frictional disc spinning at 15 RPM) was housed within the table (not under the separate dumaresq). Its rate was indicated both by a pipper in the dial plate of the dumaresq (where it could be moved to track the enemy marker in line of bearing) as well as on a scale on the table where it read against a scale of +/- 2000 yards per minute.
The tables had no bearing clock, but did not require one. The dumaresq was set up to portray the line of bearing relative to own ship's keel, and this was driven mechanically by a flexible shaft geared to the turret training ring. Therefore, as the turret trained about, the dumaresq's bearing was updated to the relative training angle. This entirely obviated the need for a bearing clock, but relied (of course), on the turret being trained on the enemy.
The spotting corrector in the 1918 handbook is significantly different from those on the larger Dreyer tables. It is smaller, incorporates a five digit Gun Range Counter (all being single digits, unlike the commonplace 00, 25, 50, 75 standard used elsewhere). A spotting handle on the side works in corrections, and three hands seem to indicate that it was also able to receive a Straddle Correction.
It lacks any means of conveying the resultant gun range to sights. Apparently, this would be manually copied over on the turret's local transmitters or simply shouted across on telaupads or voicepipes.
The range plot was very compact and similar to the Original Dreyer Table's in that the range cuts were plotted "automatically" by a pricker functioning beneath the paper when the man at the rangefinder pressed a pedal. The range on the turret's rangefinder was conveyed to the table by an F.T.P. link instrument at the rangefinder which appears to be a minor adaptation of the Range Master Transmitter. A two-position lever on the table caused this link to drive the marker across the range plot when it was in the "Auto" position. When thrown into the "Hand" position, a handle on the table could position the marker, and a knob was pressed in to cause it to prick the paper. A five digit cyclometric display on the table indicated the position of the marker in yards of range.
If ranges beyond the maximum nominally supported by the range scale were required, it was recommended that the range pencil be tuned down 10,000 yards and that plotting of range cuts be formed by hand.
The paper was 38.5 inches wide (plottable over 37.5 inches) and supplied in rolls 30 feet long.
|Early tables||Later tables||Tables s/n 81-100|
|Plotting Ranges (yards):||2,000 - 17,000||4,000 - 19,000||4,000-26,500|
|Paper speed (inches/minute):||2||2||4/3|
It seems likely to me that the move to increase the minimum range to 4,000 yards probably become ubiquitous by retrofit, and the change in scale and paper speed also a possibility after the war.[Inference] At any rate, the Handbook advises that greatly increased ranges should be supported by tuning down the clock range pencil by 10,000 yards and plotting ranges by hand rather than by the automated transmission from the rangefinder.
Rate Grid The rate grid's wires did not automatically slant to the angle corresponding to the rate on the clock as did the grids on later grids for the larger tables.
Plotting Range Cuts
Range Pencil The tables had a single red pencil to plot clock range. It could be tuned by a hand-wheel.
The tables featured no bearing plot. A simple "deflection batten" resembling a slide rule was provided instead. Presumably, this simply allowed a current deflection correction to be tracked as a form of simple tally board.
The Dreyer Handbook of 1918 and the 1930 pamphlet for the turret table lists the ships supplied with these tables, essentially battleships from the Iron Duke class onward, and battlecruisers from Tiger onward.
- Capital Ships with Tables in Turrets, 1918
|Light Cruisers with Tables in T.S.|
* = range plot scale 600 yards per inch
It would be interesting to compare these lists against those light cruisers that received the larger and more comprehensive Mark III* Dreyer Tables in their TS. Was it a matter of TS size? Number of rangefinders? Simple availability of tables?
Use of the Table
The 1913 document mentions that three men are required, but that experience may show two may actually suffice. The numbers would act as follows:
- would tune the range clock output to the mean range of the turret's rangefinder (which was to range all the time, whether in Primary or Local Control). Mention is made that when in Primary Control, the turret's range cuts would be passed to the TS after reading them "of the Range Bar of the Fire Control Instrument"
- Keeps the dumaresq (integral one, as in the 1913 design) set as ordered (matching rate indicated from TS when in Primary Control), and setting rate on range clock when in Primary
- [TO BE CONTINUED - TONE]
- Turret Dreyer Table as Fitted in the Turrets of H.M. Battleships, and in the Transmitting Stations of Certain Cruisers, 1930
- Captain F. C. Dreyer's Fire Control System for Local Control, 1913 p. 3.
- Brooks. Dreadnought Gunnery and the Battle of Jutland. p. 169.
- Captain F. C. Dreyer's Fire Control System for Local Control, 1913, Fig. 1.
- Captain F. C. Dreyer's Fire Control System for Local Control, 1913, p. 4.
- Brooks. Dreadnought Gunnery and the Battle of Jutland. p. 169, Dreyer Handbook, 1918. p. 3, and order NS14083/14, 27 March 1914, ADM 182/5, thanks to Mark Harris
- Dreyer Table Handbook, 1918, p. 81.
- Dreyer Handbook, 1918. p. 82.
- Dreyer Handbook, 1918. Plate 38.
- Pedal mentioned in 1913 document driving a "Bowden Brake" medium, which is described as pneumatic in the 1918 source.
- Dreyer Handbook, 1918. Plate 36.
- Dreyer Handbook, 1918. pp. 81-2.
- Dreyer Handbook, 1918. p. 81.
- Dreyer Handbook, 1918. p. 82.
- Handbook of Captain F.C. Dreyer's Fire Control Tables, 1918. p. 3.
- order NS14083/14, 27 March 1914, ADM 182/5, thanks to Mark Harris
- Captain F. C. Dreyer's Fire Control System for Local Control, 1913, pp. 13-14.