Invincible Class Battlecruiser (1907)

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The three Invincible class battlecruisers completed in 1908 and 1909 were the first ships of their type.

Overview of 3 vessels
Citations for this data available on individual ship pages
Name Builder Laid Down Launched Completed Fate
Indomitable Fairfield Shipbuilding and Engineering Company, Govan 1 Mar, 1906 16 Mar, 1907 25 Jun, 1908 Sold 1 Dec, 1921
Inflexible John Brown & Company, Clydebank
(Ship no. 374)
5 Feb, 1906 26 Jun, 1907 Oct, 1908 Sold 1 Dec, 1921
Invincible Armstrong, Whitworth & Company, Elswick 2 Apr, 1906 13 Apr, 1907 Mar, 1909 Sunk 31 May, 1916


The outline design based on Design "E" was approved by the Board of Admiralty on 16 March, 1905. The sheer, midship section, armour and rig drawings were approved on 22 June.[1] Uniquely, the vessels of the Invincible class were not put out for competitive tender and in late 1905 Armstrong's, Fairfield and John Brown were invited to construct the class. The Admiralty's reasoning was to prevent the closure of large private yards and thus lose Britain her competitive edge in shipbuilding.[2]


In September 1914, the ships were each to be sent eight 3/9 power telescopes and to return the same number of 2.5 power scopes, Pattern G. 329 upon receipt.  These were likely to serve as trainer telescopes.  Constrained supplies meant that 26% of the scopes actually supplied her may have wound up being 5/12 or 5/21 scopes.[3]


According to the ambitions of 1909, these ships had Service Gear Mark II wireless upon completion.[4]


In early 1913, new pattern G. 329 trainer's telescopes of 2.5 power and 20 degree field were issued to these and many other capital ships, to replace the 5/12, 5/15 and 5/21 variable power G.S. telescopes that had previously been in use.[5]

Main Battery

The four turrets were labelled "A", and "X", on the centre line and "P" to port and "Q" to starboard.[6]

This section is sourced in The Sight Manual, 1916.[7]

The eight 12-in guns were Mark X mounted in B. VIII turrets. The mountings could elevate 13.5 degrees and depress 5 degrees.

The gun sights were gear-worked sights with telescopes (not periscopes) with a range gearing constant of 48 and limited to 15 degrees elevation, but 6 degree super-elevation prisms would have been provided by 1916.

The deflection gearing constant was 70, with 1 knot equalling 2.53 arc minutes, calculated as 2700 fps at 5000 yards. Range drums were provided for 2 CRH projectiles at full charge at 2625 fps, reduced charge at 2250 fps, as well as 6-pdr sub-calibre gun and .303-in aiming rifles. By some time in 1916, dials and drums were on hand for 4 CRH heads.

Muzzle velocity was corrected by adjustable pointer between +/- 75 fps. The adjustable temperature scale plate could vary between 60 to 100 degrees Fahrenheit,[Fact Check] and a "C" corrector could alter the ballistic coefficient by at least +/- 15% and possibly 20% as in other sights.[Fact Check]

Deflection was corrected by inclining the sight bracket by 2 degrees.

The side position sighting lines were 36 inches above and 41.25 inches abreast the bore, and the central scopes were 37.5 inches above and 42 inches abreast.

Secondary Battery

Sixteen 4-in Q.F. Mark III on P. I* mounts.

The following is from The Sight Manual, 1916.[8]

Gearing constant for range is 54. Gearing constant for deflection is 56.36, with 1 knot equalling 3.17 arc minutes (2275 fps at 2,000 yards). Range dials graduated for 2325 fps, 2275 fps and .303-in aiming rifle.

M.V. corrected by adjustable pointer, +/- 50 fps. Drift correction by inclining the sight carrier arm 3.3833 degrees. Sight lines are 11 inches above the bore, and 11.8 inches aside it.

The sight was cross-connected and set from the left. A muzzle velocity cam pointer was fitted.


Torpedo Control Systems[9]

The ships had five submerged 18-in torpedo tubes:[10]

  • two on broadside forward, depressed three degrees and bearing 15 degrees before the beam; axis of tube was 5 foot 9 inches below load water line and 2 feet 3 inches above deck.
  • two on broadside aft, depressed three degrees and bearing 15 degrees abaft the beam; axis of tube was 7 foot 6 inches below load water line and 3 feet 6 inches above deck.
  • one at the stern, undepressed and with the axis of tube was 9 feet below load water line

In 1909, it was decided that ships of this class were to carry 10 heater torpedoes, distributed with six in the forward submerged flat, two in the aft, and two at the stern tube. The goal, when supplies were made good, was to have the ten heaters be Mark VI* H. or Mark VI** H..[11]

In 1913, it was approved, as part of a general reallocation of 18-in torpedoes, to replace the torpedoes on Invincible class and Warrior class except Cochrane with Mark VI** H. or Mark VI** H. torpedoes.[12]

A description of the torpedo control system for this class is found in the Annual Report of the Torpedo School, 1913. It features descriptions of adapted forms of existing Barr and Stroud instruments for torpedo order and the setting of gyro angles.

In early 1914, Indomitable and Inflexible had two Torpedo Director Pattern 2391s and two 2392s and were to have them exchanged for -A models which supported gyro angling. Invincible is not listed in this same order.[13]

Fire Control

Range Dials

As of 1920, it appears that these battlecruisers were unique in that they did not receive such equipment.[14] It may have been indicative of the belief their service would not continue much further.


The ships were completed with two 9-ft rangefinders, one in each control top. Between 1911 and 1914, a third 9-ft rangefinder was added to "A" turret, based upon their successful incorporation in later units of the Indefatigable class.[15]

Additional turret-top rangefinders were added as time went on. Inflexible had them at least from 1917 atop "P" and "Q" turrets.[16]

Sometime during or after 1917, an additional 9-foot rangefinder on an open mounting was to be added specifically to augment torpedo control.[17]

Evershed Bearing Indicators

All units were likely fitted with this equipment by late 1914.[18]

The transmitting positions were

  • Fore control platform (transmitters to port and starboard with a local switch to select one in use)
  • "A" turret
  • "X" turret
  • Upper aft conning tower

The protocols for how her crew should handle wooding of the turrets was outlined in the Handbook for Fire Control Instruments, 1914.[19]

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 a control turret. 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.. At the same time, 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.[20]

Mechanical Aid-to-Spotter

At some point, Indomitable and Inflexible were equipped with a pair of Mechanical Aid-to-Spotter Mark Is, one on each side of the foretop, keyed off the Evershed rack on the director. As the need for such gear was apparently first identified in early 1916, it seems likely that these installations were effected well after Jutland.[21]

In 1917, it was decided that these should have mechanical links from the director and pointers indicating the aloft Evershed's bearing.[22]

Gunnery Control

The control arrangements were likely as follows.[23]

Control Positions

The ships featured control positions in:[24]

  • Fore top, this being the preferred one
  • Main top
  • "A" turret
  • "X" turret[Inference]

Some ships had changeover switches within the control positions so they could be connected to either T.S.[25]

Control Groups

The four 12-in turrets were separate groups, each with a local C.O.S.[Inference] so that it could be connected to

  • Forward T.S.
  • After T.S.
  • Local control from officer's position within turret


Main Battery

The ships were fitted with a tripod-type director in a light aloft tower on the foremast along with a directing gun (in "Y" turret?).[26] The battery was not divisible into groups for split director firing.[27]

The turret Elevation Receivers were pattern number H. 2, capable of matching the 13.5 degree elevation limit of the mountings. The Training Receivers were the single dial type, pattern number 7.[28]

Secondary Battery

The 4-in broadside guns are not listed as ever having had directors installed.[29]

Transmitting Stations

Like all large British ships of the era prior to King George V and Queen Mary, these ships had two[30]

Dreyer Table

As of 1918, Inflexible still carried the Mark I Dreyer Table she'd been outfitted with.[31] Invincible was lost with her Mark I table at the Battle of Jutland. It appears likely that Indomitable never was fitted with a Dreyer table.[32]

The ships were never given Dreyer Turret Control Tables.[33]

Fire Control Instruments

By 1909, these ships were equipped with Barr and Stroud Mark II equipment for range, orders and deflection.[34]

The Handbook for Fire Control Instruments, 1909 lists the Barr and Stroud Mark II equipment on this class as:[35]

  • Combined Range, Order, Deflection: 8 transmitters, 30 receivers
  • Group Switches: 4
  • Rate: 4 transmitters, 16 receivers
  • Bearing: none
  • Range: none

Additionally, in 1909 this class had the following Graham fire control equipment:[36]

  • Turret fire gongs: 8 with 8 keys
  • Fire Gongs: none
  • Captain's Cease Fire Bells: 10 with 1 key

But by the Battle of the Falkland Islands, Inflexible's gunnery officer reported that she had Siemens fire gongs in place and "an electrical [time-of-flight instrument] which operate[d] a rattler in the control position."[37]

The ships had Target Visible and Gun Ready signals, indicating which turrets could see the target and which guns were ready in the and control positions.[38]

In 1911, it was decided that the three ships should be fitted with "range, buzzer and bearing instruments for communication between control positions, control turrets and transmitting and plotting stations."[39]

In 1916, it was approved that the Inflexible and Indomitable, should have fire control instruments fitted for their 4-in armament. Apparently they had not had range and deflection before, but it is not clear what else might be entailed.[40]

Torpedo Control

By the end of 1917, common torpedo control additions to all capital ships were to be adopted where not already in place. Those for Dreadnought and later classes with 18-in tubes were to include:[41]

  • duplication of firing circuits and order and gyro angle instruments to allow all tubes to be directed from either C.T. or T.C.T.
  • navyphones from both control positions to all tube positions
  • bearing instruments between "control position, and R.F., and course and speed of enemy instruments where applicable, between the transmitting stations and the control positions."
  • range circuits between R.F.s and control positions

See Also


  1. Roberts. Battlecruisers. p. 25.
  2. Lambert. Sir John Fisher's Naval Revolution. pp. 147-148.
  3. Admiralty Weekly Order No. 408 of 25 Sep, 1914.
  4. Annual Report of the Torpedo School, 1908. Wireless Appendix, p. 13.
  5. Admiralty Weekly Orders. 28 Feb, 1913. The National Archives. ADM 182/4.
  6. Manual of Gunnery (Volume I. Part I.) for His Majesty's Fleet, 1907. p. 1.
  7. The Sight Manual, 1916. pp. 4, 40, 106, 108-109, Plates 14-15.
  8. The Sight Manual, 1916. p. 91, Plate 43.
  9. Annual Report of the Torpedo School, 1913. Plate 53.
  10. Torpedo Manual, Vol. III, 1909. p. 265.
  11. Annual Report of the Torpedo School, 1909. pp. 13-4.
  12. Annual Report of the Torpedo School, 1913. p. 8.
  13. Admiralty Weekly Order No. 1019 of 17 Apr, 1914.
  14. Manual of Gunnery (Volume III) for His Majesty's Fleet, 1920. p. 44.
  15. Roberts. Battlecruisers. pp. 90-91.
  16. Roberts. Battlecruisers. Photo page 82.
  17. Annual Report of the Torpedo School, 1917. p. 198. (C.I.O. 481/17).
  18. Handbook for Fire Control Instruments, 1914. p. 34.
  19. Handbook for Fire Control Instruments, 1914. p. 34.
  20. Annual Report of the Torpedo School, 1917. p. 230.
  21. The Technical History and Index, Vol. 3, Part 23. pp. 25-26.
  22. Annual Report of the Torpedo School, 1917. p. 230.
  23. Handbook for Fire Control Instruments, 1914. pp. 7-8. (some inferences drawn due to fundamental differences between this design and that of Orion to which it is likened).
  24. Roberts. Battlecruisers. pp. 90-91.
  25. Handbook for Fire Control Instruments, 1914. p. 7.
  26. The Director Firing Handbook. pp. 88, 142.
  27. The Director Firing Handbook. p. 88.
  28. The Director Firing Handbook. pp. 144, 146.
  29. The Director Firing Handbook. p. 143.
  30. Handbook for Fire Control Instruments, 1914. pp. 6-7.
  31. Handbook of Captain F. C. Dreyer's Fire Control Tables, 1918. p. 3.
  32. Handbook of Captain F. C. Dreyer's Fire Control Tables, 1918. absent from table on p. 3.
  33. Handbook of Captain F. C. Dreyer's Fire Control Tables, 1918. p. 3.
  34. Handbook for Fire Control Instruments, 1909. p. 56.
  35. Handbook for Fire Control Instruments, 1909. p. 58.
  36. Handbook for Fire Control Instruments, 1909. p. 58.
  37. Verner. The Battle Cruisers at the Action of the Falkland Islands. pp. 20-23.
  38. Handbook for Fire Control Instruments, 1914. p. 11.
  39. Annual Report of the Torpedo School, 1911. p. 95.
  40. Annual Report of the Torpedo School, 1916. p. 145. Invincible was lost by the time of this mandate.
  41. Annual Report of the Torpedo School, 1917. p. 209. (C.I.O. 4212/17.).


Primary Sources

  • The National Archives. ADM 138/284.
  • The National Archives. ADM 138/285.
  • H.M.S. Vernon. Annual Report of the Torpedo School, 1911, with Appendix (Wireless Telegraphy). Copy 15 at The National Archives. ADM 189/31.
  • 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 (1910). Handbook for Fire Control Instruments, 1909. Copy No. 173 is Ja 345a at Admiralty Library, Portsmouth, United Kingdom.
  • 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.
  • 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.

Invincible Class Battlecruiser
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