British Tripod Director Firing System
The Tripod Director was the first British gunnery director generally deployed, and the one on which its capital ships relied during the Battle of Jutland.
It was a comprehensive elevation-and-training system (meaning that it sent these angles to the turrets to be matched for firing) based upon the Vickers tripod directors in "light aloft towers" or in armoured hoods. On ships featuring both types, the light aloft director was deemed the primary director in recognition of its higher placement in the ship and the presumably better view it enjoyed, despite its more vulnerable position.
The two devices were similar, but the light aloft director tower's design included the cylindrical tower and its slightly domed roof, and the armoured tower one sat within a hood whose construction and operation were intrinsic to the ship's.
The directors were tilt corrected for range (this does not mean they had cross-tilt correction) and dip to the guns was also accounted for. Moreover, drift was precisely corrected by a cam rather than the approximate correction achieved in most cases by inclining the sight.
The crew sat within a rotating tub that spun within a fixed base, facing inward to a large articulated gun sight on a tripod. It was much like a small gun mount without a gun.
There were 4 men within the light aloft director: a talker with a set of Telaupads and a voicepipe to the spotting top above, a Director Layer who elevated the sight and fired the guns, a Director Trainer who rotated the tower with either a large slewing handle or a smaller training handle, and a Sight Setter who applied the range and deflection being signaled to his F.T.P. receivers from the Transmitting Station.
In the armoured tower, a separate man below the director revolved the armoured hood by separate hydraulic means; the director itself was mechanically separate and spun within the hood, loosely matching its angle of training. Simple interlocks prevents the hood from training further off the director's angle that might cause damage to the sighting scopes.
Elevation and training was transmitted to the guns by Step-by-Step circuits to F.T.P. elevation and training receivers; elevation in steps of 1.5 arc minutes, and training angle in steps of 4 arc minutes or in a slewing mode in steps of 2 degrees azimuth which had to be used in blocks of 6 degrees.
The circuits could reliably handle 1000 steps per minute (16.67 per second), which effectively limited elevation speed to less than a half degree per second, and training to 1 degree per second and thereby eliminated the possibility of continuous aim in most conditions. Moreover, 1 degree per second in training might be so modest that firing under helm would be impossible, especially when turning against the bearing rate. Slewing mode could achieve 30 degrees per second, which would be ample for any scenario.
Firing was done by either a main or aux trigger at the director layer's hand to any number of guns that were switched in at a gun ready board worked by the talker.
In 1917, it was approved that those capital ships that did not have an armoured director hood (Iron Duke class, Tiger and earlier) should have duplicate wiring for training, slewing and elevation circuits to their aloft director, with one circuit ascending through a tripod strut and the other through the other strut or through the mast. Watertight changeover switches at the aloft director and in T.S. would permit either to be used.
- British Adoption of the Director
- British Director Firing Systems
- Admiralty, Gunnery Branch (1917). The Director Firing Handbook. O.U. 6125 (late C.B. 1259). Copy No. 322 at The National Archives. ADM 186/227.
- Admiralty, Technical History Section (1919). The Technical History and Index: Fire Control in H.M. Ships. Vol. 3, Part 23. C.B. 1515 (23) now O.U. 6171/14. At The National Archives. ADM 275/19.
- Director Firing Handbook, 1917, p. 151.
- Annual Report of the Torpedo School, 1917. p. 229. (C.I.O 3126/17.).