Gyro Director Training Gear
Gyro Director Training Gear (often G.D.T. or GDT) was a Royal Navy innovation hit upon late in the war which revisited the means by which a ship would take bearings to a target and plot them on a Dreyer Fire Control Table. GDT arrived too late to see action in the war.[Citation needed]
Monitors sometimes had to bombard targets which were themselves not visible at the director and which did not offer a distinct proxy aiming feature within a close enough firing arc. It was realized in 1916 that if the angles at the director training receiver were to be rectified by a gyro compass input, the director could indicate any angle at all and the guns could be adjusted in compass degrees from an initial salvo. Tests in General Craufurd were conducted in 1917 using parts manufactured in Excellent and in General Craufurd herself. In January, 1918, the Vice-Admiral of the Dover Patrol asked for enough equipment to have his 12-in monitors entirely outfitted. In March, 1918, an order for 24 installations was placed with Vickers.
These first devices were used for bombarding fixed land targets from an anchored monitor, and did not support a change in target compass bearing by means other than a manual adjustment, but the basic idea was pregnant enough that it was seen as offering advantages over the methods employed in capital ships in how they collected and plotted bearings for use in a naval action.
Pre-G.D.T. Methods in a Capital Ship
Before the advent of G.D.T., a Royal Navy capital ship would take bearings to the target from either an Argo Rangefinder or from a Mark VII Dumaresq situated in the armoured hood, and these would be rectified by a gyro-compass before being plotted against time on the bearing plot of the Dreyer Table. This system was not terrible, but the design suffered from the inherent defect that one's director must be on target already, so why create another pointing device and demand that its bearing angle be in agreement, and use that one to inform the fire control solution? Beyond this design fault, the old system also used a very coarse, 1⁄4 degree transmission step for the relative bearing being signaled, and this produced a very gross quantization on the bearing plot; there often seemed more noise than signal!
Once the rectified bearings were in hand, they were plotted versus time.
G.D.T. in a Capital Ship
In G.D.T., the idea was to use the director itself as the bearing-taking instrument, eliminating the possibility of observer and director being on different targets. An important incremental innovation inherent in the design was a move to adopt a new bearing transmitter that worked in 4, rather than 15 arc minute steps to improve the fidelity of the plotted data.
[TO BE CONTINUED - TONE]
- The Technical History and Index, Vol. 3, Part 23. p. 28.
- Admiralty, Gunnery Branch (1918). Handbook of Captain F. C. Dreyer's Fire Control Tables, 1918. C.B. 1456. Copy No. 10 at Admiralty Library, Portsmouth, United Kingdom.
- Admiralty, Gunnery Branch (1930). Pamphlet on the Mark III* Dreyer Table. O.U. 6196 (B). Copy at Admiralty Library, Portsmouth, United Kingdom.
- Admiralty, Gunnery Branch (1930). Pamphlet on the Mark IV* Dreyer Table. O.U. 6196 (C). Copy at Admiralty Library, Portsmouth, United Kingdom.
- Admiralty, Gunnery Branch (1930). Pamphlet on the Mark V Dreyer Table. O.U 6196 (D). Copy at Admiralty Library, Portsmouth, United Kingdom.
- Admiralty, Gunnery Branch (1930). Pamphlet on Turret Dreyer Table as Fitted in the Turrets of H.M. Battleships, and in the Transmitting Stations of Certain Cruisers. O.U. 6196 (A). Copy at Admiralty Library, Portsmouth, United Kingdom.