Dreyer Fire Control Table

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The pinnacle of fire control at the highest level in the Royal Navy during World War I was embodied in the Dreyer Fire Control Table. The tables existed in various Marks, vexingly not developed in the order of their Roman numeral Mark numbers (Mark III was first).

The Dreyer FCT in all marks was based on semi-automated plotting of range cuts and bearings versus time on separate sheets of paper and employing a dumaresq and other accoutrements to relate these data, guess their derivatives, and compute a continuous range and deflection for use at guns and/or director.

For many decades, Dreyer tables have been a scapegoat for poor shooting by the Royal Navy. This criticism is misdirected.


Dreyer Fire Control Tables were early mechanical computers ("calculating workbenches" might be a better term) meant to process data to permit a ship to engage a distant target with heavy artillery. They were fairly involved pieces of equipment, and grew more intricate between the invention of the first prototype table in 1911, their first deployment on dreadnoughts in 1912 (?) and the creation of the Mark V table in 1918. The dreadnoughts of the Grand Fleet relied on Dreyer equipment at Jutland to convert sporadic and imprecise estimates of range and bearing into workable firing parameters. Sadly, the level of success was spotty, as visibility conditions made such systematic data collection too occasional for performing the sort of graphical analysis on which the Dreyer relied.

The Dreyer FCTs were literally sturdy iron tables fitted with a number of fire control devices tied together by rotating shafts, bicycle chains and other linkages, worked by 7 or more men simultaneously as a corporate endeavour. They were housed deep within the ship in the Transmitting Station located beneath the armoured deck. By the time the Mark V table was fitted in HMS Hood, as many as 30 people might occupy the T.S., working the table and its many ancillary devices or serving as liaisons to the fighting positions of the ship. It is fair to suggest that the Dreyer and its environment and attendants resembled a premonition of the mission control centers of the Apollo program 50 years later: a human/machine system on a broad scale to factor down a torrent of real time data from sensors to create a manageable environment for exerting command at a rate a human could tolerate.

Dreyer Table as CPU in a Ship/Computer

It is not possible to study the Dreyer tables without developing a familiarity with the ship-wide art of fire control, the process of calculation and articulation by which the shells can be made to rapidly and continually fall in a pattern around a distant maneuvering enemy. The Dreyer's role was akin to that of a CPU within a modern computer system, and its "socket" was the T.S.

Examining a dreadnought as a computer system is the best way to develop this understanding. Just as a CPU processes input received via keyboard, mouse, and network adapter, the Dreyer table was given data on what the enemy appeared to be doing. And, just as a CPU might generate output on a screen or printer, the Dreyer's output peripherals were powerful naval guns. Without paying too much attention to the input and output devices, let's examine the T.S.'s role in the system by drawing a circle around it and observing which inputs and outputs crossed this membrane.

Inputs to a Mark III Dreyer Table, c1918
Input Received Source of Data Nature of Data
Observations of Target Range Optical rangefinders sporadic, imprecise
Observations of Target Relative Bearing Optical device sporadic, granular
Reports where shells are falling Verbal reports fairly often, fairly precise
Own ship's heading Gyrocompass continuous, fairly precise
Own ship's speed Forbes Log (a speedometer) continuous, fairly precise
Apparent wind speed Anemometer continuous, fairly precise
Apparent wind direction Wind vane continuous, fairly precise
Temperature Thermometer one reading suffices for the action

The outputs a Dreyer table delivered were simple and did not have far to go — nothing left the T.S., directly. Remember, the Dreyer is just the CPU... the T.S. is the motherboard, and the ship is the computer.

Outputs from a Mark III Dreyer Table
Output Generated Source of Data Nature of Data
Gun range Range clock + accrued spotting corrections continuous, 25 yard granularity
Gun Deflection Computed totals + accrued spotting corrections continuous, "1 knot" granularity

Distribution of Dreyer Fire Control Tables

As of June, 1918 Dreyer Fire Control Tables were allocated as shown:.

Table Fitted In
Mark I Dreadnought, Colossus, Hercules, Neptune, Collingwood, St. Vincent, Agincourt, Erin, Bellerophon, Marlborough, Superb, Temeraire, Australia, New Zealand, Inflexible
Mark I* Cavendish, Effingham, Frobisher, Hawkins, Raleigh, Glatton, Gorgon
Mark II Ajax, Centurion, Conqueror, Orion
Mark III King George V, Monarch, Thunderer, Excellent, Chatham Gunnery Training School
Mark III* Cairo, Calcutta, Cape Town, Carlisle, Colombo, Dehli, Dunedin, Durban
Mark IV Queen Elizabeth, Benbow, Emperor of India, Iron Duke, Tiger
Mark IV* Resolution, Revenge, Royal Oak, Barham, Malaya, Valiant, Warspite, Canada, Renown, Repulse, Lion, Princess Royal, Courageous, Glorious
Mark V Ramillies, Anson, Hood, Howe, Rodney
Turret Tables (in turrets) Ramillies, Resolution, Revenge, Royal Oak, Royal Sovereign, Barham, Malaya, Queen Elizabeth, Valiant, Warspite, Benbow, Emperor of India, Iron Duke, Marlborough, Renown, Repulse, Tiger, Courageous, Glorious
Turret Tables (in T.S. of Light Cruisers Ceres, Chester, Carysfort, Comus, Melbourne, Royalist