Waymouth-Cooke Rangefinder

Waymouth-Cooke Rangefinders, sometimes referred to as Langley Inclinometers, were hand-held devices based on the principle of the sextant rangefinder for getting a rough range estimate for purposes of station-keeping, fire- or torpedo-control.

A series of Marks were created, and found use to assist in torpedo control on ships too small for or otherwise unsuitable for coincidence rangefinders.

Early Testing

In June 1914, the captains of King George V, Orion, Hercules, and Neptune were directed to return their sextant-type rangefinder to the manufacturer to replace the long telescope with a shorter one.

In late July 1914, five were purchased for testing in Shannon, Orion, Defence, Antrim and Excellent.

Mark I

By 1918, these had been supplied one each to Vernon and Defiance as well as to twenty four light cruisers, yielding satisfactory results though the model had been superseded.

Light Cruisers with Langley Inclinometer Mark I
Penelope	Caroline	Cambrian	Birkenhead
Aurora	Conquest	Constance	Chester
Undaunted	Cleopatra	Canterbury	Dartmouth
Galatea	Comus	Champion	Weymouth
Phaeton	Cordelia	Centaur	Yarmouth
Royalist	Carysfort	Concord	Inconstant

Mark II

These could be used as rangefinders or as inclinometers. They could not focus closer than 22 feet, which presented some issues when they were to be used with Torpedo Attack Tables. This device was also dubbed the Langley Inclinometer Mark I.

As a Rangefinder

In 1917, these instruments were being given to destroyers prior to the "V" class for general purposes, as these ships had a lot of vibration and not enough room on their bridge for a coincidence rangefinder. These Mark II devices could not produce usable range estimates over 10,000 yards unless in the hands of a gifted expert. Its range scale, however, read to 18,000 yards.

As Langley Type Inclinometer

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  Photo

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  Design

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  Quadrant etchings

Twenty six Mark II devices were given additional parts to permit them to be used as inclinometers and were issued to light cruisers.

As Langley Cooke Type Inclinometer

Sextant Rangefinder Inclinometer (Langley Cooke Type)

Sextant Rangefinder Inclinometer (Langley Cooke Type)

Thirty one of these were ordered from Thomas Cooke and Sons to be given to each battleship and battlecruiser, King George V class, Princess Royal and later, and later for the torpedo schools. This was an adaptation of the Langley Type, and required the user to rotate the device about the line of sight to bring two masts (or ends) of the target into vertical alignment. When the range and base length between the features was entered on the device, the inclination would be indicated.

Handles were provided to steady the device in elevation and training, and the range scale could be set by the observer or an assistant. The eyepiece did not move with the device, counterweights balanced the affair, and large optics permitted ample light.

By 1918, all thirty one had been supplied and reported on, and a pamphlet on its use being prepared by the manufacturer. As each only came with one stand, another 28 stands had been ordered to permit them to be moved from one broadside to the other. It was an immediate success, reportedly offering:

• satisfactory results in good visibility
• early warnings of a alterations in course
• highly trained operators can do exceptionally well under lesser visibility conditions

There were, however, some alterations were requested for new manufacture, with 10 units already under order:

• Adding a fixed bearing plate and pointer to the existing stand for quick reference
• Eyepieces should be continuously variable power from 4 to 14 or lower if possible, rather than the 6 and 15 power settings in the present eyepieces.
• If continuously variable power was unworkable, three powers of 3, 6 and 15 would be good.
• Eyepieces should be further apart, and a new design to permit more light under poor visibility
• eyepieces need Kilroy rubber eyeguards, as the operators have trouble keeping both images in view at same time
• It was desired to angle the eyepieces 45 or 60 degrees downward for comfort
• integral coloured shades should be added, as they are better than slip-on glasses
• more light would be helpful, as one image is particularly dark unless the day is bright
• the vertical wire should be thinner so as not to obscure cuts, and a horizontal wire added
• the inclination arc should have 0 to 90 markings added (in red) to the existing black markings for 90 to 180, to avoid need for calculation
• eliminate present Torpedo Control Disc attachment
• adapt weight to receive slides engraved with reference lengths of British and foreign ships on both sides
• re-gear the adjustments for "Range" and "Length of Enemy" to permit faster setting
• Stops should be added to prevent "Range" and "Length of Enemy" scales from going one turn out of step
• If possible, allow length scale to vary between 50 and 800 feet
• as it is easier to use the complete length of the ship in the "displaced image principle" on a horizontal cut, allow measurements between 0 and 92 arc minutes so that it can handle
  • an 800 foot length at 10,000 yards and
  • a 100 foot portion of ship at 20,000 yards at an inclination of 160 degrees
• explore an option to displace the images vertically when inclinations are near 90

Cooke was asked which if any modifications could be made to existing articles if sent back for rework.

Mark III

They could not focus closer than 29 feet, which presented some issues when they were to be used with Torpedo Attack Tables.

The Mark III had a larger eyepiece that the Mark II, and offered a greater magnification. Its range scale read up to 24,000 yards. It was found to be useful at proportionately greater ranges, offering fair range estimates up to 15,000 yards on a clear, calm day. This improved performance, however, came at the cost of an increase in weight.

Mark VII for Horizontal Use

This was for use at longer ranges to measure total distance between masts of a ship or its total length. It could also be used as an inclinometer. When used as a rangefinder, target inclination was an input. When used as an inclinometer, the range was an input. In both cases, the class of the ship being observed had to be known to set the base scale, and this proved difficult at large inclinations.

Six devices were ordered and trialled in Castor, Parker, Calliope, Chatham, Saumarez, and Vernon.

The device's working is described in some detail in Annual Reports of the Torpedo School, 1916 and 1918.

It could not focus within 35 feet, but an new eyepieces to permit focussing at 12 feet was introduced around 1918 for use with Torpedo Attack Tables.

As a Rangefinder

Dials on Waymouth-Cooke Mark VII

A torpedo control disc or an inclination scale on its own dial would assist in factoring out the inclination of the target.

In late 1917, while awaiting the results of the ongoing sea trials, the drawbacks envisioned for the device were attributable to its rangefinding method:

• difficulty in gauging inclination accurately
• difficulty in coping with continual changes in inclination
• difficulty in guessing the class of ship being ranged upon, particularly at high inclinations
• device is difficult to manipulate, especially in poor visibility

Even so, a fleet request prompted approval that these be ordered for flotilla and half-flotilla leaders, although concern was expressed that manufacture would be slow.

As an Inclinometer

This mode of use was conceived by Sub-Lieutenant Henry F. G. Langley and Midshipman G. M. Langley and is described in some detail in Annual Report of the Torpedo School, 1916. [TO BE CONTINUED - TONE]

In 1917, the trials were not appearing very promising. The issues were:

• need to know range fairly accurately, which was difficult to achieve from small vessels. The need for accurate ranges was most keen when the inclination was near 90 degrees.
• the class of ship must be known to set the base scale, difficult as previously stated
• the difficulty of obtaining the cut at long ranges

Binocular Sextant Rangefinder

This was mentioned in passing in 1917 as having a vertical base and being suitable for destroyers. Its range and base working heads were on opposite sides and it could be worked without removing hands from the handles.

See Also

• Barr and Stroud Sine Rangefinder
• Inclinometer

Bibliography

• Admiralty, Gunnery Branch (1917). Handbook of Torpedo Control, 1916. C.B. 302. Copy No. 141 at The National Archives. ADM 186/381.
• H.M.S. Vernon. Annual Report of the Torpedo School, 1916. Originally C.B. 1329. Copy 4 at The National Archives. ADM 189/36.
• H.M.S. Vernon. Annual Report of the Torpedo School, 1917. Originally C.B. 1474. Copy 7 at The National Archives. ADM 189/37.
• H.M.S. Vernon. Annual Report of the Torpedo School, 1918. C.B. 1527. Copy 143 at The National Archives. ADM 189/38.