From: phs172m@vaxc.cc.monash.edu.au (Stephen Harker)
Subject: Re: Jutland
Organization: Physics Department, Monash University, Australia
Date: Sun, 22 Nov 1992 16:19:05 GMT


From phs172m@vaxc.cc.monash.edu.au (Stephen Harker)

In article <BxtKIu.221@law7.DaytonOH.NCR.COM>, mat@mole-end.matawan.nj.us writes:
> 
> From mat@mole-end.matawan.nj.us
> 
> In article <BxM62I.580@law7.DaytonOH.NCR.COM>, phs172m@vaxc.cc.monash.edu.au (Stephen Harker) writes:
>> From phs172m@vaxc.cc.monash.edu.au (Stephen Harker)
>  
>> 	The British gunnery was pretty good actually.  ... the British
>> [attacked] on a curving course involving high rates of change of bearing
>> and range on their own ships.  The Germans were on a stable course.  ...
>> the British ... had ...the Argo clock ... to predict the enemy's position
>> given good observations, unfortunately this was not installed and the
>> inferior Dreyer table used.  ...
> 
> Anyone care to describe these technologies?

	The _idea_ behind the technologies was to calculate the range and
bearing of the enemy ship based on past information.  It was recognised
that the only way to calculate the enemies future position was to calculate
on the basis of its past movements.  This was done using a set of
synchronous ranges & bearings (averaged over as many rangefinders as
possible) for the enemies ship to find the past movement.  The information
was to be plotted allowing your own ships movements to get a plan of the
enemies path.  The future range and angle of the enemies ship could then be
calculated, and the guns laid to compensate for the relative movements of
the two ships.  Of course a sudden change in speed or direction on the part
of the enemy would throw this off.

	Pollen recognised this answer early in the century and pushed the
development of a system to meet these requirements.  Apparently the system
he developed (the Argo clock) was superior to the Dreyer table which was
adopted, but some politics seem to have been involved there.  According to
Campbell the Dreyer table involved the following:

	A range clock which drove a pencil on moving paper.  Readings of as
many rangefinders as possible were plotted.  The clock could then be kept
in step with the mean range by visual inspection.  The rate of change of
range was determined by mechanical course and speed resolvers such as the
Dumaresq.  This required an estimate of the target's initial course and
speed, plus the spotting corrections from the salvos fired.  The Germans
only used the last two plus initial estimates from the range finders.

	In practice the German system was adequate when both sides were
moving on a parallel course, but became less accurate when considerable
movement relative to each other occurred.  The Dreyer table needed clear
visibility and long firing periods to set up accurate predictions, the
British did not have either at Jutland.  The German use of the ladder
technique together with generally better rangefinders allowed them to gain
the range quicker in the opening action, but then they had better light
also.

	According to Pollen (son of the inventor) the major advantages of
the Pollen system were that it plotted the the actual track both of your
own and the enemies ship (True Plot), whereas the the Dreyer table plotted
two separate graphs, one of ranges and the other of bearing (Rate
Plotting).  This was apparently harder to interpet and use in action.  Also
the Argo clock had a much more sophisticated method of accounting for the
ships own movements which did not lose the range and bearing despite great
amounts of movement.  This is shown by tests on the Orion, the first in
September 1912:

	This was a test of the ability to keep the range and bearing of a
fixed mark. The Argo clock was set to the initial range and bearing of the
mark and information on the Orion's course and speed fed to it during the
test.  The Orion sailed a quadrilateral course with sides between 8 and 9
miles.  Three turns were made under full helm with a total angle turned
greater than three right angles.  At the end of the test the range was
correct to 25 yards and the bearing to 0.5 degrees.

	The second test was a month later and was a battle practice test
which involved continuous firing at a distant target, while at high speed
and with high rates of change of bearing.  This involved a six point turn. 
The Orion was able to keep hitting the target through the test.  For the
time these results were astounding.

>> s...  The British ships all had, and used, director firing, the
>> Germans did use a better gunnery technique of ladder firing which found the
>> range very quickly.  ...
> 
> Or these techniques?

Bracket method:	Each salvo was spotted before thje next was fired,
		corrections were made from the spotting.  Found to be too
		slow by the British at Jutland.
Ladder method:	Two salvos fired in quick succession they were separated 
		by a known range and spotted as a pair.  This was continued
		until the bearing and range were determined.

The basis of this was the initial values for range and bearing gained by
the ships rangefinders.  Campbell says that the German stereoscopic
rangefinders were probably better than the British coincidence instruments,
but a larger base would have been better.  The Germans used 10ft
instruments.  Most of the British used 9ft instruments, but the 15" gunned
battleships had 15ft rangefinders (so did the Orion) which were much better
and gave good rangefinding.

>-----------------------------------------------------------------------

	The Great Gunnery Scandal, Anthony Pollen
	William Collins Sons & Co. Ltd, 1980, ISBN 0-00-216298-9

	Jutland: An analysis of the fighting, N J M Campbell,
	Conway Maritime Press, 1986, ISBN 0-85177-3796

-- 
Stephen Harker			phs172m@vaxc.cc.monash.edu.au
Monash University		Baloney baffles brains: Eric Frank Russell

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