Open Director Sight
An Open Director Sight is a rifle-style peep sight the Royal Navy devised for fall-back use by a turret's Officer of Quarters when telescopic director sighting systems might have difficulty finding the target in haze or poor light.
Design and Purpose
It was for installation in large gun turrets to be operated by the to direct the turret's guns, although an unsuccessful trial was conducted in 1918 to see if an altered design could be used to replace directing guns as an alternative to proper director systems.
It was also thought that it would be a helpful check that the trainer was on the correct target during individual firing. The foresight poked through the turret's roof armour through a small hole, and it moved under the actions of a sightsetter below it and by an elevation handwheel worked by the Officer of Quarters. The sightsetter had two drums (dials in some ships) – one marked in range and the other in elevation angles.When he places the desired range on the first drum, he can report the elevation indicated on the second to the gunlayers, who can elevate their guns accordingly, checking their elevations against the black pointers on their elevation receivers or by using their mechanical elevation arcs.
A pair of pistols were provided to the O.O.Q., one for each gun. These were connected, when the sight was to be used, by removing the gunlayer's own pistol wire from the interceptor and connecting the O.O.Q.'s pistol wire in its place.
The backsight had a rubber eyepiece and an iris diaphragm whose aperture could be adjusted by a milled sleeve. Drift could be accounted for by use of a milled knob to enter the range (except in Ajax, Benbow and Conqueror where drift was corrected by inclining the foresight action 2.5 degrees). A deflection knob allowed the desired deflection to then be entered. These actions both caused the backsight to move laterally atop its frame. The backsight could be removed entirely for stowage by removing a pin. The foresight was a simple metal bead. The baselength of the sight was in some cases 44 inches, and in others, 58 inches. 
22 sights were ordered in October, 1914 for complete or partial installation in 6 dreadnoughts and battlecruisers. This was soon followed by decisions to equip the entire Revenge and Queen Elizabeth classes. In July 1915, 77 more sets were ordered for general distribution in existing capital ships. Most of the installations (or at least procurement) were effected by January 1917.
- The Technical History and Index: Fire Control in HM Ships, p. 19.
- The Director Firing Handbook. p. 133.
- The Director Firing Handbook. pp. 133-135.
- The Technical History and Index: Fire Control in HM Ships, p. 18.
- 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.
- 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.