British Gunsights

British Gunsights evolved during the Dreadnought Era from simple quadrant sights to cam-worked species with telescopic, periscopic or open sight vanes which applied drift and ballistic corrections.

Developments 1890-1916

The Sight Manual lays out a brief overview of recent developments through 1916 and touches on recent innovations being considered to achieve super-elevation where ranges greater than the designed ranges must be attempted.

Sights for Transferable Mountings

In 1890, the "Bar and Drum" sight hinged at the forward wend and driven by a rack and pinion was developed for 6-in Q.F. guns. Electric lights of red or white could be shone on the open fore and back sights for night firing.

In 1900, telescopes were introduced for daytime use. Windows for electrical illumination of the cross wires were introduced. Guns with separate trainers as were then being introduced required a separate sight for him on the right side of the gun. In 1904, this requirement was obviated in 6-in P II, III and IV mountings which had cross-connected sights to permit a single gunsight mechanism to establish sighting angles to both the layer's and trainer's scopes. The P V guns had an improved sight of the same type available in 1905.

Also about 1905, adjustments for muzzle velocity which had formerly been made by shipping the correct one of a number of different range dials staggered by 25 feet-per-second differences were being made by means of replacing the formerly fixed index marks by adjustable pointers. These gave way to the cam pointer mechanisms which permitted +/- 50 fps, and then to the "Elswick" cam pointer which afforded alterations up to +/- 75 fps, the sign altering by reversing the cam, and then by a refined Elswick cam pointer which did not require flipping the cam. This last model also incorporated a temperature corrector for variations in powder magazine temperatures and it was fitted to all 12-in and 7.5-in guns and to the 4-in P III.

The cam sight was introduced in 1907, which replaced the use of rack and pinion with a cam on the range dial plate. The 4-in P II was the first gun provided one, and it added a "C" corrector to the M.V. and temperature correctors to accommodate variations in ballistic coefficient from the norm.

F.T.P. systems were introduced in the 4-in P IV guns being provided the latest light cruisers. F.T.P. was to become commonplace on future 4-in and 6-in sights.

The 6-in P IV* introduced a Free Trainer Sight, or rocking telescope holder, so that the trainer could keep his scope on the target in conditions where the sea state would otherwise pull it off. Gunnery Order 37 of 1916 directed that earlier sights be retrofitted with such gear. Gunnery Order 151 of 1915 mandated that older sights be provided open sights alongside their scopes to further assist in rough weather firing.

Sights for Turrets

Prior to 1903, turrets had vertical column sights in two sighting positions, either of which could function as the position for laying or training. The sights were inclined for drift correction, and used open sights or early telescope retrofits which required large openings in turret roofs.

Vertical column sights were replaced by trunnion sights in both 7.5-in mountings, 9.2-in Mark V and later, and in Lord Nelson and later battleships and battlecruisers. These designs kept the sight below the roof and reduced the size of the hole in the roof required. Semi-direct trunnion sights on the King Edward VII ships used connecting arms to move the sight back from the trunnion, as there was no room for it forward. This class also inaugurated the use of a third, central sighting position with sights for both guns; the outboard positions had a single sight each for the nearest gun only.

In 1906, early 12-in turrets had their guns re-sighted. The B V, VI and VII mountings had a third sighting position added with sights like the "Africa sights" in some of the King Edward VII class. The B III and IV turrets had similar sights added, as their guns were too close together to accommodate "Africa sights". The B II turrets had so little room that the side positions only got "Africa sights", and the centre position had a sight not connected to the gun at all, which must then have been only usable for training.

All trunnion sights with the exception of early 7.5-in and 9.2-in guns had M.V. and temperature correctors, and some also had "C" correctors.

In 1908, the St. Vincent class replaced the use of telescopes with periscopes. This was to become the standard scheme, as it permitted smaller sighting hoods to be used, as the man's head did not have to be poking up in the back of it to see through a telescope. Thereafter, F.T.P. receivers was the only remaining innovation to the style of sights in turrets for the Great War.

Drift correction applied automatically as the gun was elevated by a cam mechanism was being added to some sights by 1916, to replace the approximate correction previously offered by inclining the sights. Free trainer sights were added to at least one of the sights in the centre sighting positions of some ships. The trainer could use a shoulder brace to take the weight and use his torso to elevate and depress the scopes to keep the target in view.

The final wrinkle was that all ships from Dreadnought and later were retrofitted or completed with Open Director Sights for use by their Officer of Quarters.

Super-elevation Firing

For director firing, one concept considered for this was to have gun layers elevate 6 degrees in excess of the angle ordered by the director by allowing the large dial of their Elevation Receivers to range a full revolution ahead. About 5 knots of additional deflection to the left would be added (eventually from within the transmitting station) to approximate the uncorrected drift.

Another prospect suitable for telescopic sights was to provide super-elevation prisms that would cast the line of sight 6 degrees downward, and to fit these to the director or to turret sights for local firing. By 1916, one of these had been provided to all ships of Invincible class and later for use in their directors. These were accurate to within 1 minute and could be reliably shipped and landed without fear of maladjustment. About 5 knots of additional deflection would be added (again, from within the transmitting station) to approximate the uncorrected drift.

A third means was that turrets with free trainer's sights had clamps that could permit these to be locked into a 5 degree depression relative to the sight, permitting the guns to be laid from the centre position at 5 degrees super-elevation.

The open director sights added to turrets were always cut to the full elevation of the mounting, thus alleviating any deficiency in the local sights.

The 6-in P VIII and IX could have their sight arms use an alternate roller that provided 5 degrees of super-elevation. The 4-in P X mounting had a similar provision providing a full 10 degrees of additional elevation. These arrangements did not require special drift correction, as the sights on transferable mountings were inclined, and their approximate corrections were deemed sufficient.

Graduated super-elevation "strips" of some kind were provided.

Optics

Telescopes

Telescopes were often used to provide crosshairs and a magnified view of the target.

In 1907, the following types were supplied:

Pattern Number	Manufacturer	Power	Field (degs)	Diameter (in)	Remarks
1306	Ottway	3	9.5	2
1663		3	9.5	2
1663A		3 D.N.	9.5	2	Ottway illumination
1663B		3 D.N.	9.5	2.52
1697		6	9.5	2
2110A		7-21 D.N.	4.5 - 1.5	2.52
		5-15 D.N.	6.25 - 2.33	2.52
		3 to 9 D.N.	9 - 3	2.52
2110	Ross	7 - 21	4.58 - 1.52	2.52	Ross illumination
2134		5 - 12 D.N.	5.83 - 2.92	2.52
2018	—	high	—	1.153	bore sighting
2019		low

The meaning of the "D.N." designation is, allegedly, "day or night", and may mean that illumination is available though its use in this table seems odd. "V.P." is used to mean "variable power".

By 1908, it was noted that a popular scope was a day and night scope with very fine cross wires of variable power 5-21.

Other scopes in use at various times included:

Pattern Number	Manufacturer	Power	Field (degs)	Diameter (in)	Length (cm)	Remarks
?	Ottway	5 - 15	?	2.52	65	1912, from Amphion, diopter focusing, illuminated
1132		5 - 15	?	2.52	65	1916, diopter focusing, illuminated
?		6	?	2	52	1913, diopter focusing, illuminated
?		5 - 15	?	2.52	50	1917, had been diopter focusing, had been illuminated, no crosshairs, angle prism box Patt G 331
?	Ross	7 - 21	4.58 - 1.52	2.52	65	Ross illumination
?		3 - 9	?	2.52	56	diopter focusing, not illuminated, no crosshairs!

The means of shipping and testing sights and scopes for various types of gun are noted in The Sight Manual, as well as general maintenance. In particular, sights were always to be cleaned after coaling, were the special responsibility of the layer or trainer who used it when "Clean Guns" was ordered, and were to be left a low ranges when not in use.

By 1916, telescopes were focusable and marked in diopters. Each man was to know the +/- diopter setting which accommodated his personal acuity and ensure that his scopes were set accordingly so that he could avoid eyestrain that was often difficult to perceive in practice but which surely reduced a man's proficiency.

At some point, there was a Pattern 325 scope variable from 10 degrees field of view down to 3.25 degrees.

Periscopes

Periscope mode of 35 degrees and magnification 1, or, by moving a small lever to "TEL", in a telescope mode variable between 5.6 degrees at magnification 6.5 to 1.7 degrees, magnification 21. The crosshairs had to be independently focussed by a ring near the eye piece.

There was a wiper fitted to clean the exposed lens window, but these did not work well at all. Rather, the windows could be cleaned from within the turret by removing the blast excluder and tilting up a rain hood — a condition that crews in non-superimposed turrets were invited to leave in place if they chose. Better than the wipers were two lines to blow air and fresh water onto the window. Tinted caps for the eyepiece of smoked or green glass could be fitted if helpful when firing against a bright light, sun or searchlight. Periscopes were to remain shipped with waterproof covers atop and silk bags in place at both ends, but the blast excluders were only to be fitted when firing to avoid straining the mechanism. Side sights were to be left at high power setting, as this was judged to be the most accurate except when trying to acquire a target. One of the two centre sights was to be left at low power to assit the trainer when considerable seas were running.

See Also

• F.T.P.

Bibliography

• Template:BibUKSightManual1916