Sentinel Class Cruiser (1904)

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The eight scout cruisers of the Sentinel class (or Scout class) were completed in 1905.

Today, the class described here is often considered as being four separate two-ship subclasses (Sentinel, Pathfinder, Forward and Adventure), but contemporary documents treat them as a single class most of the time, and so we do here.


In 1912 and 1913, four Bastian Radiators were obtained for a temporary trial in warming the Officers' Cabins on the Upper Deck where radiators were not already present in Boadicea. Based on the satisfactory reports, these radiators were kept in place permanently and in December 1913, their installation in the Sentinel class.[1][2]


In January 1914, it was reported that a rangefinder mounted on the fore upper bridge may have been unable to work properly when the ships were steaming at high speeds. Whether this was due to vibration or spray is not made clear.[3]


As built:

  • Ten 12-pdr guns
  • Eight 3-pdr

After 1911/1912:

  • Nine 4-in Q.F. Mark IV guns on P. IX mountings (4 on each broadside, 1 on C.L. aft)
  • Six 6-pdr

4-in Guns

The 4-in guns provided for all eight ships were Q.F. Mark IV on P. IX mountings.[4]

The mounting could elevate to 20 degrees and depress to 10 degrees, but the sight could only elevate 15 degrees and was graduated to just 12.5 degrees (7,900 yards full charge). It is likely that extended range strips were provided at some point to allow at least 15 degree elevation to be achieved.[Inference] Thereafter, prisms might have permitted 20 degree firing after 1916 or so.[Inference]

The sight was an F.T.P. gear-worked design with a range gearing constant of 26.66 and range dials provided for 2200 fps and 1-in aiming rifle. M.V. could be corrected by a cam pointer which allowed for a decrease to 2000 fps.

The deflection gearing constant was 52.6 with 1 knot equal to 3.18 arc minutes, corresponding to 2200 fps at 2000 yards. Drift was corrected by inclining the sight about pivot pins 2 degrees.

The layer's telescope sight line was 12.5 inches above the bore, and 21.45 inches left. The trainer's telescope sight line was 12.5 inches above and 17.4 inches right. Open sights were 13.3 inches above the bore and 24.35 inches left for layer and 20.3 inches right for trainer.

The sight had a temperature correcting scale plate and a "C" corrector.

The layer had an open sight. The trainer's sight could be used as a free sight with a counterweight.


  • Two 18-in torpedo tubes, above water

Fire Control

Evershed Bearing Indicators

This equipment was unlikely to have been fitted for gun or searchlight control.[5]

Control Groups

"Scout" class Gun Control Groups[6]

In 1909, these were described as being similar to the Gem class, but the forecastle and poop guns could be controlled as separate groups or attached to the nearest broadside group on either side. The middle line guns could be connected to whichever side was desired.[7]

When the armament was converted to nine 4-in guns, the general control means created 4 groups:[8]

  1. No.1 gun port and starboard (these guns could be split out into groups 2 and 3)
  2. Port guns 2-4
  3. Starboard guns 2-4
  4. Aft CL gun (this could be thrown into group 2 or 3)

Voicepipes permitted this scheme to be blurred further if required.

Torpedo Control

Transmitting Stations

The ships had a T.S. with two C.O.S. and four sets of transmitters.

Dreyer Table

These ships had no fire control tables.[9]

Fire Control Instruments

Fire Control Systems[10]

By 1913, after their light 12-pdr armament had been traded in for 4-in guns, these ships were equipped with Vickers Mark III F.T.P. instruments for their sightsetting. The arrangements are documented in the Annual Report of the Torpedo School, 1913.[11]

Their T.S. was equipped with four sets of fire pushes and transmitters with repeat receivers:

  • panel "A" addressed No. 1 guns port and starboard
  • panel "B" addressed the aft, CL gun
  • panel "P" addressed port guns Nos. 2-4
  • panel "S" addressed starboard guns Nos. 2-4

There were two The two No. 1 guns were wired through C.O.S. No. 1 with repeats on the gun side which had 3 positions, of which number 2 was regarded as useful only for switching over cleanly between positions 1 and 3:

  1. both No. 1 guns on "A"
  2. No. 1 gun port on "A", No. 1 starboard on "S"
  3. No. 1 gun port on "P", No. 1 starboard on "S"

The change-over was synchronised in this manner when splitting the guns for broadside fire:

  1. get "A" repeat receivers to the same range and deflection as "S"
  2. switch C.O.S. 1 to position 2
  3. work "A" to match No. 1 port's repeats to 'P'
  4. switch C.O.S. 1 to position 3

The aft CL gun was wired through the second C.O.S. with repeat receivers on the gun side. It also had 3 positions:

  1. aft gun on "B" (its own)
  2. aft gun on "S"
  3. aft gun on "P"

The guns had continuous ringing fire gongs, and the fire pushes were wired through the

Voicepipes connected the control positions to the T.S. and to all guns. This could be used in parallel with the instruments to further divide fire.

See Also


  1. Admiralty Weekly Order No. 600 of 24 October 1913.
  2. Admiralty Weekly Order No. 741 of 19 Dec, 1913.
  3. Admiralty Weekly Order No. 790 of 9 Jan, 1914.
  4. The Sight Manual, 1916. pp. 80, 108, Plates 33, 34.
  5. The Technical History and Index, Vol. 3, Part 23. p. 29.
  6. Handbook for Fire Control Instruments, 1909. Plate 54.
  7. Handbook for Fire Control Instruments, 1909. pp. 51-52.
  8. Annual Report of the Torpedo School, 1913. p. 112.
  9. Handbook of Captain F. C. Dreyer's Fire Control Tables, 1918. p. 3.
  10. Annual Report of the Torpedo School, 1913. Plate 64.
  11. Annual Report of the Torpedo School, 1913. p. 112.


  • 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 (1918). Handbook of Captain F. C. Dreyer's Fire Control Tables, 1918. C.B. 1456. Copy No. 10 at Admiralty Library, Portsmouth, United Kingdom.

Sentinel Class Scout Cruiser
Vickers/Sentinel Group
  Sentinel Skirmisher  
Cammell Laird/Pathfinder Group
  Pathfinder Patrol  
Fairfield/Forward Group
  Foresight Forward  
Armstrong/Adventure Group
  Adventure Attentive  
<– Gem Class Minor Cruisers (UK) Boadicea Class –>