View source for Waymouth-Cooke Rangefinder

'''Weymouth-Cooke Rangefinders''' were hand-held devices based on the principle of the [[Sextant Rangefinder|sextant rangefinder]] for getting a rough range estimate for purposes of [[Station Keeping|station-keeping]], [[Fire Control|fire-]] or [[Torpedo Control|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 Rangefinder|coincidence rangefinders]].<ref>''Annual Report of the Torpedo School, 1917'', pp. 199-200.</ref>

==Mark II==
These could be used as rangefinders or as inclinometers.

===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.<ref>''Annual Report of the Torpedo School, 1917'', p. 199.</ref>  Its range scale, however, read to 18,000 yards.<ref>''Annual Report of the Torpedo School, 1917'', p. 200.</ref>

===As Langley Type Inclinometer===
<gallery>
File:ARTS1917Plate57.jpg|Photo<ref>''Annual Report of the Torpedo School, 1917'', Plate 57.
File:HandbookTorpedoControl1916AppendixPlate1.jpg|Design<ref>''Handbook of Torpedo Control, 1916'', Appendix Plate 1 on page 98. </ref>
File:HandbookTorpedoControl1916AppendixPlate2.jpg|Quadrant etchings<ref>''Handbook of Torpedo Control, 1916'', Appendix Plate 2 on page 99. </ref>
</gallery>

Twenty six Mark II devices were given additional parts to permit them to be used as inclinometers<ref>''Annual Report of the Torpedo School, 1917'', p. 197.  See also ''Annual Report of the Torpedo School, 1916'', p. 26 (no copy known to exist)</ref> and were issued to light cruisers.

===As Langley Cooke Type Inclinometer===
[[File:ARTS1917Plate58.jpg|thumb|240px|'''Sextant Rangefinder Inclinometer (Langley Cooke Type)'''{{NEEDEDPORT}}<ref>''Annual Report of the Torpedo School, 1917'', Plate 58. {{NEEDEDPORT}}</ref> ]]
[[File:ARTS1917Plate59.jpg|thumb|240px|'''Sextant Rangefinder Inclinometer (Langley Cooke Type)'''{{NEEDEDPORT}}<ref>''Annual Report of the Torpedo School, 1917'', Plate 59. {{NEEDEDPORT}}</ref> ]]
Thirty one of these were ordered from [[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.<ref>''Annual Report of the Torpedo School, 1917'', p. 198. (C.I.O 2097 of 1917 -- N.S. 15024/17)</ref>
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.

==Mark III==
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.<ref>''Annual Report of the Torpedo School, 1917'', p. 200.</ref>

==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|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.<ref>''Annual Report of the Torpedo School, 1917'', pp. 197, 200.</ref>

Six devices were ordered and trialled in [[H.M.S. Castor (19xx)|''Castor'']], [[H.M.S. Parker (19xx)|''Parker'']], [[H.M.S. Calliope (1914)|''Calliope'']], [[H.M.S. Chatham (1911)|''Chatham'']], [[H.M.S. Saumarez (19xx)|''Saumarez'']], and [[H.M.S. Vernon (Torpedo Training School)|''Vernon'']].<ref>''Annual Report of the Torpedo School, 1917'', p. 197. (C.I.O 1974-- N.S. 15178/17)</ref>

===As a Rangefinder===
[[File:HandbookTorpedoControl1916AppendixPlate3.jpg|thumb|240px|'''Dials on Weymouth-Cooke Mark VII'''<ref>''Handbook of Torpedo Control, 1916'', Appendix Plate 3 on page 100. </ref> ]]
A [[Torpedo Control Disc|torpedo control disc]] or an inclination scale on its own dial would assist in factoring out the inclination of the target. (TODO: ARTS 1916, p. 26 and plate 3 )

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.<ref>''Annual Report of the Torpedo School, 1917'', p. 200.  (N.S. 28,228/17)</ref>

===As an Inclinometer===
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.<ref>''Annual Report of the Torpedo School, 1917'', p. 200.</ref>

==See Also==
* [[Barr and Stroud Sine Rangefinder]]

==Footnotes==
{{reflist}}

==Bibliography==
{{refbegin}}
*{{BibUKHandbookOfTorpedoControl1916}}
*{{BibUKARTS1917}}
{{refend}}

[[Category:Fire Control]]
[[Category:Torpedo Control]]
[[Category:Shipboard Equipment]]