Sentinel Class Cruiser (1904)

The two scout cruisers of the Sentinel class were completed in 1905. This class is sometimes considered as one of four 2-ship subclasses (broken down by builders) of the Scout class cruisers.

Overview of 2 vessels
Citations for this data available on individual ship pages
Name	Builder	Laid Down	Launched	Completed	Fate
Sentinel	Vickers, Barrow	8 Jun, 1903	19 Apr, 1904	Apr, 1905	Sold 18 Jan, 1923
Skirmisher	Vickers, Barrow	29 Jul, 1903	7 Feb, 1905	Jul, 1905	Sold 3 Mar, 1920

Armament

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 CL aft)
• Six 6-pdr

4-in Guns

The 4-in guns provided for all eight scout cruiser were Q.F. Mark IV on P. IX mountings.

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.

Torpedoes

• 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.

Control Groups

"Scout" class Gun Control Groups

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.

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

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.

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.

Fire Control Instruments

Fire Control Systems

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.

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 C.O.S.es. 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 C.O.S.es.

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

• Wikipedia

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 (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

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