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Concentration is the practice and method of having more than a single ship fire upon the same target. Although the practice offers clear benefit in allowing a superior force to make good its advantage in strength, difficulties each firing ship faces in correcting its fire undercuts the effect.

Innovations in procedure and equipment during the war allowed fire to be joined with ever-diminishing loss of effectiveness due to mutual interference and confusion.


In early 1913, trials of special "Cruiser Arc Lamps" pattern 1875 to convey range, rate and target signals that had been conducted in the Home Fleets were soon to be concluded.[1]

History and Signalling

September 1915 Orders

By 1915, a Gunnery and Torpedo Order[2] indicated that "concentration in pairs has given the most satisfactory results and should be the usual procedure." Firing in threes or fours was noted as a possibility, if greater possibilities of confusion were to be accepted. Reliance on director firing and use of time-of-flight watches was seen as fundamental in keeping spotting straight.

It was hoped that alternative salvos would somewhat naturally result, or that it could be sorted out. Intercommunication between adjacent ships had proven a failure as there was no one to attend to it. An outline of abbreviated signals to be communicated by morse flag "signalling disc" or lamps between control tops was nonetheless specified, other ships were to be called up by their pendants.

Message Signal Example
What is your GUN RANGE Interrogative G
GUN RANGE is (range in 100 yards) G GUN RANGE is 15,500 155 G
What is your RANGEFINDER RANGE Interrogative F
RANGEFINDER RANGE is (range in 100 yards) F RANGEFINDER RANGE is 13,700 137 F
What is your DEFLECTION Interrogative D
DEFLECTION is (number of knots left) LT DEFLECTION is 10 knots left 10 LT
DEFLECTION is (number of knots right) RG DEFLECTION is 6 knots right 6 RG
What is your RATE Interrogative R
RATE is (yards opening) O RATE 250 opening 250 O
RATE is (yards closing) C RATE 100 closing 100 C
What SHIP are you firing at Interrogative S
  tenth ship from the right R 10
  second ship from the left L 2
  third ship of Kaiser class 3 KR
  second ship of Konig class 3 KR
  first ship of Helgoland class 3 KR
  second ship of Nassau class 2 NU
  third Battle-cruiser 3 BC
  third Cruiser 3 CR
  second Light-cruiser 2 LC
What SHELL are you using Interrogative SH
  Lyddite Common LYC
  Powder Common PC
  A. P. AP
Submarine 6 points to starboard Green Flag Sign 6
Mine on port bow 7 P
Mine ahead W 7
Torpedo approaching bearing 30 Red T 30 R
Torpedo approaching bearing 90 Green T 90 G
Signal received RD
No answer can be given Z

February 1916 Orders

In February 1916, a new code was introduced, replacing the earlier one.[3] It was functionally similar to the previous one. Ships were to be called up by their pendants.

Message Signal Example
What is your GUN RANGE Interrogative VX
GUN RANGE is VX (range in 100 yards) GUN RANGE is 15,500 VX 155
What is your RANGEFINDER RANGE Interrogative VY
RANGEFINDER RANGE is VY (range in 100 yards) RANGEFINDER RANGE is 13,700 VY 137
What is your DEFLECTION Interrogative VK
DEFLECTION is VK (number of knots left) DEFLECTION is 10 knots left VK 10
DEFLECTION is (number of knots right) VK DEFLECTION is 6 knots right 6 VK
What is your RATE Interrogative VR
RATE is (yards opening) VR RATE 250 opening 250 VR
RATE is VR (yards closing) RATE 100 closing VR 100
What VESSEL are you firing at Interrogative VL
  tenth ship from the right 10 VL
  second ship from the left VL 2
  Distinguishing signals could be used to indicate the class or battle squadron of the enemy
What SHELL are you using Interrogative VP
  Lyddite Common VP 1
  Powder Common VP 2
  A. P. VP 3
Enemy altering course to starboard VM (number of compass points)
Enemy altering course to port VN (number of compass points)
I am about to fire at your target VQ
Enemy is zig-zagging, turning together VZ (number of compass points)

May 1917 Orders

By May 1917,[4] a committee had convened to discuss this issue and resulted in enlarged set of rules and procedures for flashing light communications between control tops. The code was expanded, and rendered the previous one obsolete. It was stressed that no squadrons should customise the code in order that commonality might be preserved. Four copies of the code was to be provided each ship, to be posted on weighted boards to ensure that they'd sink should they fall overboard.

The battleships and battlecruisers were to be equipped with two lamps, one arranged forward to be usable from red 120 to green 120 and one aft to face aft to work from green 120 to red 120, worked from the fore T.S. or from the adjacent compartment in those ships where the fire control W/T set were located there so they could be worked together. The lamps were to be made from searchlight projector barrels (24-in would suffice) with twelve 50 candlepower incandescent lamps replacing the arc lamp. Both lamps and a buzzer to be heard at the light would be jointly controlled by the single morse key in T.S. below. Each lamp was to be attended by two experienced signal ratings, one to read incoming signals and transmit them to fore T.S. by buzzer, telephone or range and order transmitter, and the second to train the lamp on the intended friendly vessel and monitor the local buzzer through "listeners", in order to permit failures in the circuit to be quickly detected and reported. A "Smith's lamp" or Cruiser Arc Lamp would be provided as a fallback in case the lamp went.

The lamps were to communicate:

  • which ship was to be engaged (i.e., bearing, class of ship, number that enemy's ship occupies in the line, etc)
  • mean rangefinder ranges before opening fire
  • hitting ranges after opening fire
  • rate, when asked for
  • deflection, when asked for
  • details of the ladder

The visual signaling system was expressly not to be used for purposes other than fire control, such as to warn of approaching torpedoes.

The W/T code was to be identical to the flashing lamp one, but it was not subject to the above limitations.

No signals were to be acknowledged, and only some answered. Signals were made without previous call or preamble, nor was the customary VE procedural sign to be used to end a signal nor any Executive signs to be used. Service call signs were used, and ranges were transmitted in hundreds of yards.

There is an extensive code to document here. [TO BE CONTINUED - TONE]

Sequence Firing

Basically, there were two methods developed to concentrate fire on the same target without mutual interference. The first (and less complex) was sequence firing, referred to as GIC in the Royal Navy for its three-character signal code. In this method, ships coordinated and fired in a fixed time slot sequence, with one ship firing while the other was reloading. With careful attention to time slots, a ship could spot her salvos while ignoring other ship’s salvos in the “off” time slots. Ships exchanged gunnery data, but each ship spotted and controlled her own fire. It required steady communication for coordination and could be used by ships with different size main batteries. However, the fixed time sequence limited the effective rate of fire and was more appropriate for extended range salvo time of flight. The normal, occasional delays in reloading one or more main battery turrets and temporary visibility obstructions for spray, smoke, etc. could cause a ship to miss her sequence. Further, it prevented the normal process in which a ship would correct salvos until the target was straddled and then fire several salvos as quickly as possible before repeating the spotting process to “get on” again. These limitations meant sequence firing was generally effective only for pairs of ships (additional ships further reduced the effective time slots and accentuated rate of fire limitations) at long range. GIC firing procedures were standardised in the Royal Navy after Jutland for capital ship divisions. Following the November 1917 cruiser clash with the German High Seas Fleet, this practice was extended to light cruisers which had been equipped with centralised director fire control.

Master Ship Firing

The other method was massed firing, referred to as GMS in the Royal Navy. One ship acted as the master ship and controlled the fire for all participating ships, enabling multi-battery salvos and larger ladders to get on target quicker. Since one ship was determining the fire control solution, all participating ships had to have the same type of main battery and robust communications to quickly pass range and azimuth corrections for succeeding salvos to each ship. It had the advantage of rate of fire flexibility and larger salvos and was not limited to long range. But, it required intensive training and frequent practice by the participating ships to be effective and fast, uninterrupted communications to work. This was largely beyond WWI technology. In addition, the increased number of splashes from multi-battery salvos was more difficult to correctly spot. In early 1918, Cdr. H. E. Kimmel, a USN observer with the Grand Fleet, confirmed to the USN General Board that massed firing trials had been practically abandoned, “That was a failure.” He added that sequence firing “...shows promise of considerable development.”

Post War Refinements

After the war, all navies pursued the promise of concentration fire and developed the required W/T communication technology and firing techniques to maximize its application. Range clocks and turret azimuth marks were developed to enhance intercommunication and became prominent in interwar photographs. The Royal Navy’s 1939 Firing Manual noted that GMS was, “…the standard system and is used by all ships armed with similar guns and equipped with similar fire control tables.” GIC was an alternate method for ships with different batteries and ships from different divisions, which had not practiced together.

The USN pursued a slightly divergent course developing dye colored shells to differentiate salvos through the use of different colors for each ship. Practice brought proficiency and confidence in this approach was evident in the USN Battleship Doctrine of the late 1930s. “In concentration fire, when spotting projectiles are being used, ships will proceed without regard to each other, as in the case of single or ship-for-ship fire. When spotting projectiles are not used, ships in concentration will fire in rotation beginning with the concentration leader, but no ship will wait appreciably more than one half-salvo interval for a preceding ship to take its turn. When ships are firing in rotation, a ship must not fire a salvo within five seconds of another ship’s salvo.” Given that anything but “short” splashes were extremely difficult to spot at long range, it would seem color dye shells were planned to be used primarily with aerial spotting.

The Royal Navy also pursued spotting projectiles. The British colored dye mechanism, called a “K device,” was based on a French pre-WW II design that proved defective and had to be redesigned. This delayed the issuance of “K shells” (5.25-in and larger) until mid 1942, by which time there was little opportunity for employment.

By the eve of WWII, all navies had developed concentration fire procedures and practiced them frequently until they were confident their ships were ready to use them should the tactical situation arise. But like most other things, it proved much harder to achieve in the stress and confusion of battle than it had been in the many pre-war training exercises. The Royal Navy quickly noted that the frequent drills and practice needed to ensure effective coordination were hard to maintain with ships continually steaming in anti-air and anti-submarine escort operations. Combining warships into last minute ad-hoc divisions for an operation became the norm, which also hindered ships working together long enough to develop the required teamwork. These trends reached a nadir in June 1944 when Admiral Lee had to decline a potential engagement because his fast battleships had been too busy escorting aircraft carriers to practice their traditional gunnery skills. Further, there were few daylight engagements between forces large enough to create the numerical superiority situations that called for concentration fire. Thus, actual examples of concentration fire were fairly rare.

See Also


  1. Admiralty Weekly Orders. 28 Feb, 1913. The National Archives. ADM 182/4.
  2. Grand Fleet Gunnery and Torpedo Orders. pp. 30, 31. Nos 65 & 66. 600-15/9/15.
  3. Grand Fleet Gunnery and Torpedo Orders. No. 132 of 11/2/16, p. 50.
  4. Grand Fleet Gunnery and Torpedo Orders. No. 236 of 22/5/17, pp. 119-122.


  • Brooks, John (2005). Dreadnought Gunnery and the Battle of Jutland: The Question of Fire Control. Oxon: Routledge. ISBN 0714657026. (on and
  • 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.
  • Much of this article taken from research provided by Lonnie Gill