490 PRACTICE SEAWARDS. 
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bring our ten knot boat^into a range of c 1,000 yards we at once* double 
her angular speed, and thus represent for onr gun layer a twenty knot 
boat at 2,000 yards. So far as angular speed is concerned then a 
faster target is not a necessity if we will only bring our target in 
closer. 
Angular speed is only of great importance in the training of gun 
layers. Let us clearly distinguish it then from other conditions and 
fire some of our rounds at say 600 to 1,000 yards range to train gun 
layers. 
Rate of Change of Range. —This affects the B.C. as regards the 
range correction he orders, beyond that not at all. It considerably 
affects the G.Gf.C. in judging what length of prediction he shall give. 
It does not affect the gun layer, and does not much affect range takers. 
It is evident then that the rate the range changes is of chief impor¬ 
tance to the G.Gf.C. and that only in a matter of drill: actual firing 
is not necessary to teach him how to predict. For drill purposes the 
rate of change of range may be increased by putting false heights on 
the range finder. For instance if the true height is doubled the rate 
of change of range is doubled. In other words a ten knot ship be¬ 
comes apparently a twenty knot ship. 
So far as actual speed is concerned then I think we can train effect¬ 
ively with our present targets on the lines I show. But there is 
another point in connection with the running past attack, which is 
of the utmost importance, and on which we get little experience. 
This point is the total amount the range changes during practice. At 
present the total alterations in range are very small. A condition for 
the Centenary Cup is that the difference between the maximum and 
minimum ranges must be 250 yards. This is a small change in eleven 
minutes. B.C.’s now find their “ corrections ” and once found need 
not alter them ; they are getting no experience of how to vary their 
“ corrections” as a target closes on them. Furthermore this point is 
of the utmost importance to range takers. It is not generally recog¬ 
nised that the focus of the object glass of their telescope varies with 
the range, and that as the target closes they must alter their focus. 
With the practically constant range of our present peace target this 
necessity is not realised. To show the importance of this I may men¬ 
tion that from a height of 30 feet: if a man focuses on a datum 1,200 
yards away, and then tries to pick up the range of an object 3,700 
yards away without refocusing his object glass, he may have any error 
up to 6°/ c of the range. This 6°/ 0 means 200 yards and may be either 
plus or minus. Of course this percentage error varies with the 
height and the range. At greater heights however, the permissible 
errors of the guns are less, and the question of re-tocus of the object 
glass remains important. 
Can we get targets that will give us a large variation between max¬ 
imum and minimum ranges ? I think we can, but at the expense of a 
certain amount of rate of change of range. This sacrifice does not 
appear to be very material. 
