Iron Duke Class Battleship (1912)

Overview of 4 vessels
Citations for this data available on individual ship pages
Name	Builder	Laid Down	Launched	Completed	Fate
Benbow	Beardmore	30 May, 1912	12 Nov, 1913	7 Oct, 1914	Sold Mar, 1931
Emperor of India	Vickers	31 May, 1912	27 Nov, 1913	10 Nov, 1914	Sunk 1931
Iron Duke	Portsmouth Royal Dockyard	12 Jan, 1912	12 Oct, 1912	10 Mar, 1914	Sold 2 Mar, 1946
Marlborough	Devonport Royal Dockyard	25 Jan, 1912	24 Oct, 1912	2 Jun, 1914	Sold 27 Jun, 1932

Radio

According to the ambitions of 1909, these ships had Service Gear Mark II wireless upon completion.

Searchlights

The ships were fitted with Crompton's 24-in twin projectors. In 1914, some or all of these were to be modified to permit 90 degree elevation for use in anti-aircraft work.

Armament

Main Battery

This section is sourced from The Sight Manual, 1916 except as otherwise noted.

In April 1915, the 13.5-in Mark V(H) guns were in Mark II* mountings except in Benbow, which had Mark III* mountings (though it is possible that later these were updated and all mountings acquired a second star). The mounts were able to elevate 20 degrees and depress 5 degrees. Benbow and Empress of India had 100 rounds per gun and Iron Duke and Marlborough 80 rounds plus 6 shrapnel. Each gun had a 6-pdr sub-calibre gun for practice.

The sighting arrangements were similar to those in Tiger and the King George V class.

The sights were cam-worked and limited to 15 degrees elevation, but the central sights had "20 degree super-elevation strips". Additionally, 6 degree super-elevation prisms would have been provided by 1916. The deflection gearing constant was 61.3, with 1 knot equalling 2.51 arc minutes, calculated as 2500 fps at 5000 yards.

Range drums were provided for full charge at 2450 fps, three-quarter charge at 2000 fps, as well as 6-pdr sub-calibre gun and .303-in aiming rifle. Muzzle velocity was corrected by adjustable scale plate between 2560 and 2260 fps. The adjustable temperature scale plate could vary between 40 to 100 degrees Fahrenheit, and a "C" corrector could alter the ballistic coefficient by +/- 20%.

The periscope holder was inclined 1 degree 37 minutes (which may have effectively been 2.5 degrees for mechanical reasons; it equalled .195 degrees correction at 10,000 yards).

The side sighting scopes were 43.25 inches above and 39 inches abreast the bore. The central scopes were offset 56.25 inches above and 42 inches abreast.

OOQ open director sights capable of 20 degrees elevation were to be fitted sometime following 1916.

The guns were capable of continual aim in all but heavy weather. Gunlayer and turret trainer each used a single hand wheel. Elevation was at 5 degrees per second was achieved by just a single revolution of the hand wheel — a final increase in sprightliness over King George V and Lion classes.

6-in Battery

The ships mounted twelve 6-in Mark VII guns in P. VIII mountings, two on the main deck and ten on the upper deck.

After the Battle of Jutland, when alterations to increase protection forced weight-savings to compensate, the ammunition allotment for these guns was to be reduced to 140 rounds per gun and 6 shrapnel rounds.

Other Guns

• Four 3-pdr Hotchkiss guns on Mark I* mountings on the flying deck.
• One 3-in Mark I gun on a Mark II H.A. mounting on the shelter deck.

Immediately before the start of war, the 3-pdr Mark I* mountings on Iron Duke and Marlborough (at least) were be given spring eyepieces.

Torpedoes

Four 21-in broadside tubes, the forward ones bearing 80 degrees and the aft tubes bearing 100 degrees.

Fire Control

Range Dials

As of 1920, all four ships were equipped with a Range Dial Type B and a Type C.

Phones and Voicepipes

In early 1914, the Iron Duke (at least) had a voicepipe between T.S. and G.C.T..

Secondary Battery

Navyphones for 6-in Fire Control

Each of the six 2-gun groups was on its own navyphone circuit, feeding a Pattern 2464 Navyphone for the group officer as well as a pair of Telaupads for each gun. These led to six 2-way C.O.S.es in the 6-in TS which would dictate whether the given 6-in group's phones were tied to either

1. the Pattern 2463 Navyphone and its associated Pattern 2465 transmitter
2. the single 2464 in the G.C.T. for its broadside.

Additionally, when the C.O.S. was in position one, each group's panel in the T.S. had a grouping switch so that any transmitter could address either or both of the other groups on its broadside. See the notes on the gunnery groups to see how this loosely mimics the fire control instruments.

Rangefinders

A drawing of the ship in Burt's British Battleships seems to imply that initially, each turret carried a 9-ft rangefinder in its roof.

The T.C.T. rangefinder, initially a 9-foot instrument of unknown model, sat on an M.Q. 8 mounting.

In 1916-1917, a "medium-base" length rangefinder was added over the conning tower.

Sometime, likely not before 1918, these were to be upgraded to 15-foot instruments, with new armoured hoods and racers and training driving the hood directly rather than through the rangefinder mounting. These rangefinders lacked hand-following gear to facilitate in transmission of range cuts, and when it was considered as an addition around 1917, space concerns were causing issues.

By 1918, two additional 9-foot instruments were also to be provided for torpedo control, abreast the captain's sea cabin, except on Iron Duke, where they were placed on either side of the lower chart house platform, displacing a pair of 23-in signalling searchlights to the compass platform.

By 1918, the ships had:

• two 25-ft in turrets (presumably in "B" and "X")
• one 18-ft in a turret (presumably in "A" or "Y")
• one 15-ft in a turret (ditto)
• one 9-ft in a turret (presumably in "Q")
• one 9-ft (in forward superstructure, likely the one adding 1916-1917)
• one 15-ft in T.C.T.
• two 9-ft in fore bridge (likely the torpedo control ones alluded to above)
• two 2m F.T. 29 high-angle RFs

In 1920-1, a 12-ft rangefinder was added over the T.C.T. in the aft superstructure, and a "long-base" rangefinder added to the rear of "X" turret. Between May 1928 and May 1929, Iron Duke had a "small" rangefinder added on a high platform on aft superstructure, possibly to make up for the wholesale removal of the T.C.T. from her and Marlborough in 1927.

Evershed Bearing Indicators

All four units were likely fitted with this equipment before late 1914.^[Inference]

However, it is clear that all 6-in guns had a bearing indicator fitted. This strongly implies that a rich installation supported the main battery at least.

Otherwise, one might reasonably assume the particulars resembled those of the King George V class.^[Inference]

In 1917, it was approved that capital ships of Dreadnought class and later should have Evershed equipment added to their C.T., able to communicate with either the fore top or the G.C.T.. If there were not enough room in the C.T., a bearing plate with open sights and 6-power binoculars would be added to the C.T..

Also in 1917, it was decided that all directors were to be fitted with receivers and, "as far as possible", ships were to have fore top, G.C.T. and controlling turrets fitted to transmit as well as receive, though this was noted as being impossible in some earlier ships. While it would have been nice to have the C.T. able to transmit bearings to the 6-in guns, it was decided not to do this for reasons of space.

Mechanical Aid-to-Spotter

At some point, all ships in this class were equipped with four Mechanical Aid-to-Spotter Mark IIs:

• one on each side of the foretop, driven by flexible shafting from the Evershed rack on the director
• one on each side of the Gun Control Tower employing an electrical F.T.P. system.

As the need for such gear was apparently first identified in early 1916, it seems likely that these installations were effected well after Jutland.

Gunnery Control

The control arrangements were as follows.

Control Positions

Main battery:

• Gun control tower
• "B" turret
• "X" turret

Each 6-in broadside:

• G.C.T. (abreast conning tower)
• Alternative positions aft (Groups 1 & 2 from one, group 3 from a second one)

Some ships had C.O.S.es within the control positions so they could be connected to either T.S..

Control Groups

The five 13.5-in turrets were each a separate group with a local C.O.S. so that it could be connected to

• Transmitting Station
• Local control from officer's position within turret

The 6-in guns were formed into three 2 gun groups on each side, and the circuits for each side are led through one of two 3-way C.O.S..es offering the following modes:

1. each group on that broadside worked by its own transmitters in the TS
2. the broadside as a whole is connected to the adapted Vickers range clock situated in its 6-in GCT
3. each group on that broadside is connected to the alternative control position, where (1? 3?) portable range-and-deflection transmitters with tell-tales are used.

See the section below for a diagram.

Directors

Main Battery

Training and Elevation Circuits

Training and Elevation Circuits

Firing Circuits

The ships were fitted with a cam-type tripod-type director in a light aloft tower on the foremast along with a directing gun in 'X' turret.

The main battery could be divided into forward ("A", "B" and "Q") and aft ("X" and "Y") groups for split director control.

A C.O.S. in the T.S. afforded these options:

1. All turrets on aloft tower
2. All turrets on directing gun
3. Forward group on aloft tower, aft group on directing gun

Secondary Battery

The ships had a pair of directors fitted to port and starboard on the forward superstructure to direct the 6-in broadside guns. Marlborough's were pedestal-mounted, and the others tripod-mounted.

Transmitting Stations

Like Tiger and possibly later ships,^[Inference] these had a T.S. for the main battery and another for the 6-in secondary battery. It is not clear to me whether the secondary battery's TS had a Dreyer table.

Dreyer Table

In June 1918, Marlborough had a Mark I Dreyer Table while the other three units had Mark IV Dreyer Tables and all had been provided Dreyer Turret Control Tables. The disparity in Dreyer Marks creates a loose impression that all ships were initially given Mark I tables and for some reason Marlborough missed her chance for an upgrade, perhaps due to her damage at the Battle of Jutland.

At some point, the ships each received Dreyer Turret Control Tables, but it is unclear when and whether each turret received one or simply the two control position turrets.

Fire Control Instruments

Indicator Lamp and Gong Circuits

Continuing the pattern established in the Colossus class, all 4 units used Vickers F.T.P. Mark III range and deflection instruments to the gun sights (except Mark III* in the 6-in T.S. panels) and Barr and Stroud (probably Mark II* or later^[Inference]) instruments for other purposes.

The Mark III F.T.P. range receivers on the 6-in guns were fitted with Usborne Accelerating Gear. An adapted Vickers Range Clock similar to that used in the Mark I Dreyer Table could be employed to relay ranges to the 6-in guns. An operator on the clock would have to follow-the-pointer to transmit the ranges. Each 6-in broadside had its own independent Captain's cease fire gong circuit. Firing keys were Pattern 872, and each gun had a fire gong.

The ships also had Gun Ready signals in the T.S. and control positions, but had no Target Visible signals.

In 1916, it was approved that the ships should have a range rate transmitter/receiver pair between TS and spotting top for the main armament. Additionally, it was ordered that Lion and King George V classes and later should receive instruments such that the fore top could be interchangeable as a gun control position with the GCT.

The ships were perhaps the first to be provided Kilroy Turret Training Indicators.^[Inference]

Secondary Battery

Diagram of 6-in Fire Control

A description of the fire control system for the 6-in guns is found in the Annual Report of the Torpedo School, 1913.

Torpedo Control

By the end of 1915, all four ships had been equipped with a Torpedo Control Plotting Instrument Mark II in their T.C.T..

In 1916, a number of further changes were decided upon:

• Navyphone communication between C.T. and aft torpedo flat and T.C.T. and fore torpedo flat
• removal of secondary director hoods
• "transfer of instruments in the secondary positions" to the C.T. and T.C.T.. I presume that "secondary positions" means the secondary director hoods.
• it was approved that the ships should have a transmitters in the T.S. and receivers in T.C.T. and C.T. so that gunnery data for range, course and speed could be shared with the torpedo control group.
• arrangements were to be made that all capital ships with 21-in torpedoes to receive transmitters and receivers so that the T.C.T. could pass the plotted torpedo deflection to the C.T., which could then use a reciprocal set of equipment to send the T.C.T. a deflection to be placed on the sight and range to open fire.

By 1917-1918, a number of common Torpedo Control equipment packages were to be provided to those ships not already sporting them. Those for the 21-in torpedo ships follow.

Torpedo Control Data between C.T. and T.C.T..

The data instruments to be wired between C.T. and T.C.T. to share range, order and deflection data provided a single deflection transmitter in the T.C.T. so that the results of the torpedo plot to be sent to the single deflection receiver in the C.T. for the information of the Torpedo Control Officer. Conversely, a combined range and deflection transmitter forward allowed the T.C.O. to send back the deflection and intended firing range to the secondary T.C.O. in the T.C.T..

Torpedo Control Evershed

The 21-in torpedo ships were also to be provided with Evershed transmitters in the C.T. and a receiver at the torpedo rangefinder in the T.C.T. in order to ensure that it was obtaining data on the intended target. Limited "slit space" in the C.T. required that the customary binocular-based transmitters be foregone in favour of placing the transmitter on or below the floorboards and to drive it by a shaft from a Torpedo Deflection Sight Mark IV. A control key on the transmitter allowed it to indicate when it was controlling the remote rangefinder or not.

Those ships in the First Battle Squadron, as were these, also were to receive bearing and inclination instruments between the C.T. and fore spotting top to allow the Torpedo Control Officer to send the target bearing to the spotting top so that men there could signal back the inclination of the target.

Finally under the 1917-1918 mandate, sufficient instruments were to be provided to permit the Fore Bridge to communicate with the tubes.

See Also

• Wikipedia
• 3D Model available for licensing

Bibliography

• H.M.S. Vernon. (Feb 1914) Annual Report of the Torpedo School, 1913, with Appendix (Wireless Telegraphy). Copy 42 at The National Archives. ADM 189/33.
• 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 (1914). Handbook for Fire Control Instruments, 1914. G. 01627/14. C.B. 1030. Copy 1235 at The National Archives. ADM 186/191.
• Brooks, John (2005). Dreadnought Gunnery and the Battle of Jutland: The Question of Fire Control. Oxon: Routledge. ISBN 0714657026. (on Amazon.com and Amazon.co.uk).
• 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, 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.