Royal Navy’s 6 inch Cruiser

H.M.S. EDINBURGH and H.M.S. BELFAST were the heaviest of the triple gun turret 5 inch cruisers at 10,420 tons, others were between 8,500 and 9.500 tons.
Ship Data.
Length 613 ft. Beam 63 ft.4 in. Draught 17 ft.3 in.
Shaft HP 80,000 0 300rpm Max Speed 32 Knots
Armoured Belt 4.5 inches thick
Crew 381 to 956 if the Flag was on board.

Armamment after modernisation:-
4 triple 6 inch turrets
6 twin 4 inch mountings
5 twin 40 mm Bofors.

The Main Armament.
The 6 inch Breech Loading Rifled gun was first fitted in a Royal Navy ship on an upper deck mounting in the early 1800’s. The first 6 inch gun to be fitted in a twin gun turret was in a Monmouth class armoured cruiser at the turn of the century.
The triple gun turrets designed between the wars weigh about 135 tons, there are two right guns and one left gun, each weighing nearly 7 tons and there is a crew of 46 men to each turret.
The ships outfit of shell is 2862 rounds, the shell weighs 112 lbs. and the cordite charge is 30 lbs.
The maximum range is 25,480 yards with a muzzle velocity of 2760 ft./sec. and a rate of fire of 8 rpm/min for each gun. With four turrets this represents 5 tons of metal and explosive fired every minute.
The gun is rifled with a right hand twist of 32 grooves. The breech mechanism has an interrupted thread screwed breech block requiring about 35° of a turn to lock it closed.
Each gun has its own ammunition supply hoists and all machinery is hydraulically powered, the pumo is driven by a 374 HP electric motor.
The turret is suspended on a roller path just below the gun house floor and is prevented from lifting when firing by clips round the upper and lower roller paths.
Going down from the gun house is the working chamber, the cable winding gear, shell room and at the bottom, the cordite handling room and the magazine.

Cordite Magazine and Handling Room.
The cordite is supplied in silk bags in a cardboard container which is stowed in leather covered cork stowages. The cardboard container of cordite is passed through flashtight scuttles to the cordite handling room where the bottom of the cordite hoists are. The hoist is a simple endless chain hoist with small flashtight buckets to take the cordite up to the gun house.

The Shell Room.
The shells are stowed in wooden racks in the shell room where there is also the shell ring attached to the ships structure for the transfer of shells to the revolving structure. From the shell ring shells are loaded into the bottom of the shell hoists. These are similar to the cordite hoist but have more control interlocks.

The Cable Winding Space.
Over the shell room is the cable winding gear which enables all the hundreds of power and control cables to pass from the fixed ships structure to the revolving structure of the turret. Batteries for low power supplies are also at this level and in the working chamber above is a small low power switchboard.

The Working Chamber.
The working chamber houses most of the machinery for powering and controlling the various machines in the turret. All of the hoists, gun elevation and turret training drives have hand/power change over clutches in this space for use in event of power failure.

The Gun House.
The training compartment is quite a small compartment where the turret can be controlled and fired independently in an emergency. Three operators, the trainer who trains the turret, the sight setter and layer control the local sight.
When the shell reaches the top of the hoist it is tilted on to a tray where it is slid and swung into line with the breech and rammed by hand.
The cordite is removed from the cardboard container and placed on the shell tray for ramming by hand rammer. The breech is closed and when all is ready all guns fire together in a broadside. On firing the gun recoils about 18 inches, and is buffered by an air filled recouperator. The gun is controlled in recoil and run out by an oil filled recoil cylinder. After firing and when the breech is re-opened a blast of air is blown up the barrel to clear it of any fumes and the chamber is washed with a fine soray before reloading.
The captain of the turret’s position is at the rear of the gun house where he has a periscope and his communication operator.

Development of Fire Control.
Having loaded the guns it is imoortant to aim them accurately and to fire them at the right moment. During the opening years of this century the greatly improved accuracy and increased range of the gun required improvement in aiming and control.
A Director system was developed and trials carried out on H.M.S.NEPTUNE in 1911. This was followed by a computing mechanism called a Dumaresq which was a timing device enabling a rate of change of range and deflection to be calculated. A timing device known as the Vickers Range Clock was also produced with gave an increment of range of the target.
The next step was to combine these two mechanisms into one when the Admiralty Fire Control Table was Produced by Elliot Bros, and fitted in H.M.S. NELSON and H.M.S.RODNEY in 1923. This basic design, though modernised, was. still fitted to Leander class frigates for surface fire control until their turrets were removed during modernisation over the last 15 years or so.
There was no control for Anti-Aircraft fire until 1930 except hose pipe fire with tracer.

The Surface Gun Control System.
The main pieces of equipment in the 5 inch Surface Fire Control System are:
Look Out Sights
Gun Direction Officers Sight
Operations Room
2 Director Control Towers
The Transmitting Station.

The Director Control Tower,
The director can be directed on to a surface target from the GDO sight visually or the Ops room radar. The director will then track the target visually. Range can be measured by radar or estimated visually.
The director has a crew of seven. The director is moved in training and elevation by electric motors. In addition to this movement the layers and trainers binoculars are stabilised in elevation by a gyro controlling a hydraulic pilot valve which in turn controls a hydraulic motor driving the sights.

The Transmitting Station
This compartment has a crew of 15 and the main niece of equipment is the Admiralty Fire Control Table.
This table is about 10 ft. long, 3 ft. wide and 3.5. ft. high. The top half contains all of the calculating mechanisms required to produce gun elevation and gun training to each turret. Hand wheels are for making the initial settings and for manual operation in the event of a power failure. The arrow on the toD indicates the line of sight so that every thing rotates around that.
In the lower half is a constant speed electric motor which provides the time element. The calculating mechanisms are driven by seven hydraulic motors which are powered by an external pump.
Sight elevation and training and present range are transmitted from the director to the fire control table where calculations are carried
out. Own, enemy and wind speed and direction are resolved into speed along and speed across the Line of Sight. These are integrated to
range and distance across respectively.

Corrrections for Training.
Target course and speed during time of flight.
Own ship course and speed
Wind speed and direction
The drift of the shell.
These corrections added to Sight Training and line spotting produces Gun Training. A further correction is added to allow for convergance
due to the displacement of each turret from the director.

Corrections for Elevation.
Range corrections due to:
Target course and speed.
Own ship course and speed.
Wind speed and direction.
Ballistics (type of shell, temperature of cordite etc.)
Atmospheric conditions.
The present range plus the range corrections produces gun range. This is fed to the Tangent Elevation mechanism, then added to Sight Elevation to become Gun Elevation. This is then transmitted to each turret. However this is not correct for every gun, further corrections have to be made in the elevation receivers in the turret as follows:-
Dip – for the displacement of each turret from the director.
Tilt – for the variations in the deck plane.
Difference in muzzle velocity of each gun.

After firing a broadside, changes in enemy course end speed are detected by the speed across and error in range plot against those generated by the table. Errors are measured by the slope of the plots and transferred to cross wires over the enemy ship dial to indicate a new enemy course and speed. Further suggestions would also be made by the spotting officer in the director or from radar as spotting corrections.
Other types of calculating mechanisms used in the table are:-
Differentials – bevel, rack and lattice.
Multipliers – screw, rack sector and lattice.
Vectors – screw and cam resolvers.
Trigonometrical funcations – sine/cosine Tangent resolvers.
Integrators – ball and potters wheel.
D.W. Shead,