A METHOD OF EVALUATING CORRECTIONS IN 
THE CASE OF QUICK TARGET^ 
BY 
LIEUT.-COLONEL J. E. J. JOCELYN, 
An important, if not the only function of many forts in war, will be 
the prevention of swift vessels running past them. Corrections for 
travel of target, often further complicated by considerations of tide, 
will then be of great moment, and must be quickly evaluated and 
applied; and, as guns will be laid over the sights, whenever possible, 
their responsibility will rest, entirely, on the officer controlling the fire. 
The method of determining corrections for travel, by drums or 
tables, based upon a “ change of range,” is simple and expeditious, 
and in certain cases is capable of easy application, but it is open to 
question if it could be made use of, against a very rapid objective 
steaming straight on to a fort, or nearly so. Then, ranges would change 
very rapidly, corrections would have to be made again and again, an 
officer would not only have to estimate the error of his last shot, but 
would have to consider how corrections would be modified by the then 
position of the target. At night “ snap shooting” might have to be 
used, the enemy being only visible at intervals, and at any time, smoke, 
either from the fort or the ship, might prevent observation of fire, 
which would be liable to further interference, from the difficulty of 
identifying projectiles, if several works were simultaneously in action. 
In certain waters, also, new complications would be impressed upon 
all the foregoing, if tides were variable and sites were low. 
To cope with these difficulties, not only great natural quickness 
appears necessary, but considerable practice is also desirable, which, 
unfortunately, is difficult or impossible to get, owing to safety con¬ 
siderations and the present pace of towing. 
Moreover, it is probable that ammunition, if properly sorted and 
gauged by trial shots, can be trusted; that guns shoot even more 
accurately than the range tables affirm ; that errors in racers and other 
gear can be detected and allowed for; that, after a little training, few 
mistakes are made in loading, or in giving elevation and group differ¬ 
ence ; that reliable layers are forthcoming; and that, in general terms, 
the success of the shooting depends upon the officer controlling the 
fire and his range-finding instruments and detachment. 
Now, it is in the defence of channels, straight or nearly so, that the 
difficulties of correction, above referred to, approach the acute stage; 
the following method is an attempt to turn these very conditions to 
account, so that corrections may be laid dozen beforehand and applied^ 
after the manner of a group difference . 
1. VOL. XXI. 
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