range finder on dreadnaughts

[DeadlyDaring]

Can someone point me to the direction of some in depth info on the Secondary range finder (range clocks) on all dreadnaughts etc

EG: Trailing ships often did not have as good a view of the enemy as the leader, but could observe where the leaders guns were aimed (and read numbers from the range clock) in order to set initial values for aiming their own guns.


Cheers
DeadlyDaring

[DeadlyDaring]

9 have visited
yet you dont know ....
then WHY visit ....
someone will have an answer


Cheers
deadlydaring

[David]

These large 'clocks' are commonly called range clocks, though the British called them concentration dials. Developed towards the end of WWI, they were part of a system to concentrate the fire of several ships onto the same target.

In the days before WWII, the most accepted formation for battleships was the line of battle, where ships would line up nose to tail and fire broadsides at the enemy. The British found that due to the poor visibility in the North Sea, further hampered by funnel and gunfire smoke, it was fairly rare for all the ships in the line of battle to actually see the enemy. So large dials resembling clock faces were added to the front of the fore mast, and to the rear of the main mast, trainable to 30 degrees off center. These clock faces were solid white disks (though a couple of ships had open centers) with black numbers from 0-9. Similar to a clock, there was a short hand and a long hand; the short hand was blue with a diamond at the end, and the long hand was red with a circle at the end.

Once a ship found the range to the target, it would display the range on the dials, with one hand indicating thousands of yards + 10,000, and the other hundreds of yards. So if both hands were on the 1, the range to target was 11,100 yards. Hash marks, called bearing indicators, were painted on the main gun turrets, giving observers the angle to target. With the range and bearing data from the ship in front or behind them to feed into their range keeping tables (fire control computers to us Yanks), and the proper adjustments made for the distance between the ships, their location in formation, etc, the gunnery officers on a battleship could target their guns on an enemy they could not see with a fair degree of accuracy. They could then pass the information on to the next ship in line, allowing the entire battle line to concentrate fire on an unseen enemy.

These range clocks were fitted to British, American, Brazilian, and French battleships and cruisers. However, as first radio communication, and then radio-equipped spotting aircraft allowed for the instant and accurate transfer of targeting information, these clocks were phased out. By the dawn of WWII, only a few ships still had them, mostly the older American dreadnoughts. As each went into the yard for a refit, the clocks were removed.

[revwardoc]

David,

How effective were these "clocks"? I read that at Jutland British marksmanship left quite a bit to be desired.

[David]

Concentration Dial or Range Clock - In many ship photographs taken between about 1916 and 1940, there are what appear to be large clocks on the front and rear superstructures or masts. These are actually devices to tell the other ships in the formation at what range that ship is firing at. Together with Declination Marks, these mechanisms allowed the other ships in the formation, whose view of the target may be obscured by fog, gun smoke or funnel smoke, to have their guns at the proper elevation and bearing when their view becomes unobstructed. This greatly reduced the time needed before they were ready to fire.

The introduction of radar and better ship-to-ship communication methods in the late 1930s eliminated the need for these devices and they were removed from most ships by the start of World War II or shortly thereafter. For the concentration dial shown here, the small hand represents the range in thousands of yards, with 0 = 10,000 yards and 9 = 19,000 yards. The big hand represents range in hundreds of yards.

Declination Marks - Scales painted on a turret mount to indicate to other ships in the formation the direction in which the turret is pointing.

[David]

Looking up at the main armament & bridge work of the California (BB-44) in dry dock at Hunters Point Naval Ship Yard in 1936. Note the concentration dial, or "Clock".

The practice of gunnery at the beginning of the 20th century put a lot of emphasis on shooting first. Radio communications was cumbersome, morse code, slow and visual signals, light, flaghoist or semaphore, were not much better. When an enemy was detected it also took time to train and elevate the guns to shoot at him. In poor visibility this might give him the first shot. The range clocks, and their companion, the deflection markers, were developed to shorten the time needed to get off the first salvo.

Concentration of fire was also a major consideration, and usually all ships of a division would fire on the same target. Fire control was based on mechanical analog devices that incorporated input from the optical range finders located at several places on the ship. In USN ships this included the top of the cage mast.

Long range visibility under battle conditions was often poor. The heavy black smoke from burning coal just made it worse. But individual ships could be expected to have a reasonably clear view of the next ship ahead in the division line. The flagship was almost always in the lead, and could direct concentration of fire by passing range and deflection data to the other ships. This process was made much faster by simply training the flagships own guns in the direction of the enemy and displaying the ships own average rangefinder results on a circular display. Trailing ships often did not have as good a view of the enemy as the leader, but could observe where the leaders guns were aimed (and read numbers from the range clock) in order to set initial values for aiming their own guns.

There was no CIC as we know it today, but there was a central fire control plot on each ship. This plot included a MECHANICAL device for determining and transmitting refined settings for azimuth and elevation of the guns. Initial inputs were often set manually. Communications between the plot and the gun turrets (and the range clocks) included up to 4 separate and parallel methods. First, there was a mechanical connection, usually a bicycle chain and sprocket drive to ensure equivalent movement. Second, voice tubes connected the plot with rangefinder positions and guns. Third, when they became available, there were internal communications telephones matching the above circuits. Finally, if other means failed, you could write a note and send it by messenger.

As a final note range "clocks" are numbered from 1 to 10, not 1 to 12. The figures were usually given in thousands of yards.

[David]

The Vickers Range Clock was a clockwork device used by the Royal Navy for continuously calculating the range to an enemy ship.


In 1903, Percy Scott described a device he'd invented which was similar to the Vickers clock. In April 1904 Vickers worked with Scott and patented their device, samples of which were available for trials in 1905. In 1906 the Royal Navy ordered 246 units for use on their ships. More than one might be installed, to allow for tracking multiple targets.

The device consisted of a circular dial with a single central rotating pointer, like a clock. The dial was engraved with the ranges in yards. The clockwork motor drove the pointer at a constant rate determined by a control on the right hand side of the device. This had a handle and its own dial, on which the rate of change of range (or "range rate") could be selected. This was calculated by other means, often by use of a Dumaresq or a time-and-range plot. A second rotating handle was fitted to the left of the clock. This was connected by gears to the dial plate, which rather than being fixed as on a clock, could be rotated. One turn of the handle would rotate the scale 100 yards relative to the pointer. Thus the clock could be set to the initial range to a ship, or corrections could be made to update the reading without disturbing the mechanism.

The range on the dial was the range as passed to gunners for firing, and as such included any corrections necessitated by time of flight, wind, etc., rather than being a true instantaneous record of distance to the enemy. By 1913 a second red pointer had been added to the original black one, attached to it by a friction grip, which could be adjusted relative to the original hand, so that one indicated true range and the other the corrected range for targeting.

Once some shots had been fired, spotters would report the fall of shell (which could be observed because of the large waterspouts where the shells hit the sea) and the range would be corrected up or down depending whether the shells were short or over the enemy. Initial estimates of range were obtained using optical rangefinders.

The dial was fitted with three separate scales reading 2,000-6,000 yards, 6,000-10,000 and 10,000-14,000 yards in 100 yard steps, with marked subdivisions every 25 yards. The handle for adjusting the dial was added from 1908; previously the initial position of the dial plate had to be set by rotating it directly. Initial models had the rate setting dial calibrated in both knots and 'seconds per 50 yards'. This was altered in 1909 to yards per minute, which standardised measurement was used on other equipment designed to work with the clock.

An important aspect of the Vickers range clock, as well as other designs using a wheel-on-disc drive for the variable speed motor, such as the electrical clock used in the Dreyer Fire Control Table, was that it could only generate ranges according to a constant range rate. In most firing scenarios, the range rate would change continuously. In such cases, the operators of the clock would periodically alter the range rate in discrete increments as conditions suggested.

Mechanism

Variable speed was obtained using a rotating metal disc driving a rubber wheel resting against it. The position of the wheel could be moved in and out along a radius of the disc, so that the wheel turned at different speeds (faster the further out). Operating errors would occur from adjusting the wheel, as the wheel tended to slide as it was dragged across the face of the spinning disc as it was adjusted. The workaround adopted was to adjust the rate quickly and in a discrete manner, accepting that the generated ranges would deviate moderately from the desired continuous hyperbolic curves that predominated in use. In 1909 alterations were made to the clockwork drive to improve reliability of the governed speed and to increase the power of the drive.

A small aperture on the dial would reveal a visual tell-tale which indicate that the clock's spring required winding.