The main visible wartime development was director control for secondary batteries, first proposed for the two latest battlecruisers Queen Mary and Tiger. In January 1915 director control was ordered for all ships with 6in secondaries. Like main-battery directors, these were small vertical cylinders; ships typically had one on each side.
Another important wartime director development was gyro-controlled fire, work on which began in February 1915. A prototype was fitted to Centurion in September 1915 and an improved version to Iron Duke in March 1916. That month C-in-C Grand Fleet asked that all director-controlled ships be fitted with gyros as soon as possible. Production began in April 1916, before the first formal orders were let (22 August 1916).
The spotting position was separate from the director. When ships were fitted for director control of their secondary batteries, that entailed both installation of additional directors and also a new control (spotting) position, typically much lower than the spotting top, because the secondary guns fired at a shorter range.
In January 1915 Admiral Jellicoe (who as DNO had strongly advocated the director) pointed out that experience had shown that director fire was significantly slower than independent fire when conditions were favourable, particularly in ships with quick-acting elevating valves and (hydraulic) presses. The director waited until all guns were ready and then waited for the right moment to fire. It offered advantages only under some difficult conditions – in half light, at night, in thick weather and in rough weather when gunlayers suffered spray interference. A ship could fire more rapidly if guns were independently aimed, compensating for the ship’s roll by continuous aim. The greater the range, the greater the importance of the director. Conversely, a Royal Navy fighting at shorter ranges could exploit its greater ability to maintain continuous gun aim to get a higher firing and hitting rate. Ships with directors had to be prepared to use independently-aimed fire.
On the other hand, the director could help solve the problem of target designation. The captain on the bridge or in the conning tower chose the target. He had to get that information to the guns and to the separate fire-control party aloft – not to mention to the transmitting station below. Once firing began, the numerous enemy ships would be shrouded in gunsmoke. What if guns and controllers were concentrating on different targets? The control party would try to correct fire against one target on the basis of splashes from shots fired at the other. The ship would never hit anything. Jutland showed that the director was only a partial solution. Ships were provided with Evershed Bearing Indicators (EBIs) so that the CO could designate a target to the director by passing its bearing.
Fire control required accurate range data. Dreadnought and her immediate successors had 9ft rangefinders in their spotting tops (typically they are not visible in photographs). This type of rangefinder was installed on board all ships up to the 1911–12 programme (Tiger and Iron Dukes). Additional rangefinders were fitted in turrets for local control in the event that the main rangefinder was knocked out. This installation was approved by mid-1912 for new super-dreadnoughts, beginning with the King George V and Queen Mary classes. In 1913 installation was approved for all battleships, but it began only with the outbreak of war. At that time, Orion and earlier dreadnoughts had only one turret rangefinder and Lion and Princess Royal had only two. Ships of later programmes were completed with a rangefinder in each turret. In 1914 the turret rangefinder programme was incomplete, HMS Lion having the greatest number. Director control helped ensure that all turret rangefinders were pointing at the same target. Once ships had multiple rangefinders, their data had to be averaged to improve accuracy.
The rangefinder atop the conning tower was introduced in the 1909–10 ships (Lion and Orion classes). It later ships it was an armoured stabilised rangefinder (Argo mounting, Barr & Stroud coincidence instrument). Beginning with the Queen Elizabeth class, the armoured hooded rangefinder was converted into an armoured director.
The Queen Elizabeth and Royal Sovereign classes were completed with the improved 15ft rangefinder. It was installed on board other ships after the outbreak of war. These classes had 15ft rangefinders in each turret and in the armoured control tower and two 9ft rangefinders (foretop and torpedo-control tower).
In October 1915 Admiral Jellicoe asked that new capital ship designs incorporate longer-base rangefinders than the current 15ft: a longer base translated into reduced range error.16 At this time ships typically had 15ft rangefinders in their turrets, 9ft rangefinders in the armoured hoods atop their conning towers and 12ft rangefinders aloft in their spotting tops. The aloft rangefinder was considered the largest which could occupy that position. It appeared that in existing ships the 9ft in the armoured hood could not be replaced by a 15ft instrument as in the 15in battleships. The largest rangefinder then in prospect was a 22ft type which could be built out of tubes similar to those used for the 15ft. A 28ft instrument did not enter production because it would have to be made in three pieces. On 11 December 1915 DNO asked that new capital ship designs incorporate a long-base rangefinder outside the control tower, the rangefinder in the tower being omitted. On 7 February 1916 Controller approved one 22ft rangefinder for any new capital ship design.
As redesigned in 1916–17 Hood introduced a 30ft rangefinder to deal with much greater ranges. She had 30ft rangefinders in each turret and in the armoured hood above the conning tower, a 15ft rangefinder in the foretop and two 15ft rangefinders for torpedo control (on two directors between the funnels and on one torpedo-control tower aft). In October 1917 further orders were given so that each capital ship would have two long-base rangefinders (orders totalled seventy-one 30ft and twenty-four 25ft), but none of the new rangefinders had been delivered by the end of the war.
A major visible wartime development was equipment to assist in concentration firing, in which some ships might be firing at a target they could not see. Ships were fitted with range dials, to indicate their firing ranges and their turrets were marked so that others in a group could see the bearings at which they were firing. The range dials recalled pre-war range drums which similarly displayed ranges at mastheads.17 In addition to the visible fittings, ships had Type 31 gunnery radios intended to pass range and other data.
The post-war solution to ensuring co-ordination of rangefinding, control and the director, first employed in the abortive 1920 capital ships and then in the Nelsons, was to combine the two functions in a director control tower (DCT) carrying both director and rangefinder. The DCT was associated with a new-generation analogue computer, the Admiralty Fire Control Table (AFCT). The DCT could not be supported adequately by a tripod mast. Instead, it had to be mounted atop a tower bridge. The tower foremast/DCT combination appeared in all of the abortive capital ship designs of the 1920s, in the new battleships and in the massively rebuilt Queen Elizabeths and Renown. However, in 1940 Hood had her foremast director converted into a lightweight DCT in its original position atop her tripod mast. Capital ships which did not get new bridge structures had neither the new type of DCT nor its accompanying AFCT.
Guns were aimed on the basis of assumed enemy current range, course and speed. A miss showed that the original estimates were incorrect. The observed error had to be fed back to correct the original estimates of enemy course and speed. What the spotter saw – how far off the shots were – depended on both enemy speed and course, neither of which was measured directly. The fire-control system had to predict target position both to aim the