298 
QUICK-FIRING GUNS IN HARBOUR DEFENCE. 
Rate at 
which 
Ranges 
change. 
the range to begin with, in doing which he would receive 
considerable assistance if the Fort Commander were to 
send down to him the range as given by his own range- or 
position-finder, at the same time that he points out the 
objective. 
The “ Group Commander ” would pursue a system much 
the same as that adopted in ranging a Field Battery at a 
moving object. Suppose, for example, the ship to be 
approaching the battery. All the guns take up the range 
given on the dial, which would be some 100 or 50 yards 
short of the estimated range of the ship. The leeward gun 
would then be signalled to fire a ranging shot. If this 
be observed to fall somewhat short, the same gun will again 
fire after a short interval—if the shot were observed very 
short, the elevation of the group would first be increased. 
When the “ Group Commander” observes a ranging shot 
to fall close to the ship he signals “ Rapid fire,” whereupon 
all the guns pour in their fire at the utmost possible speed; 
until the “ Group Commander” perceives several shot to 
fall over or burst high on the upper works of the ship, 
when he orders “ Cease fire,” reduces the elevation shown 
on the dial, and orders “ Slow fire ” again from the ranging 
g'un, and “ Rapid fire” when the ship comes to the new 
range. This he would continue, taking care that the 
differences of elevation are not so great as to cause serious 
delay in the fire. For a ship moving away from the group 
he would fire ranging shots over, and range again as soon 
as he saw his “ rapid fire ” shells striking the water on the 
near side of the ship. 
Against this it may be urged that a modern fast ship, such as these 
guns would be likely to engage, may be moving at the rate of some 
22 miles an hour, or nearly 650 yards in a minute. But this does not 
mean that her range is altering at that rate—that would only occur 
when she is running straight in on the battery, which is not likely if 
she moves at this tremendous pace. This excessive speed could only 
be attained when the hostile ship is trying to run past the shore 
defences, and under these conditions the rate at which the range alters 
would not be nearly so great; the change in the cruiser’s range would 
probably not exceed 300 yards per minute for any course that she is 
likely to take. And if we consider only the freeboard of the vessel 
and shots fired at one elevation, we see that she is likely to be hit by 
them whilst the range changes by nearly 100 yards. For the mean 
freeboard, in graduating index plates for guns in elevated batteries, is 
taken as 14 feet. Taking as an example a 4*7-inch gun firing at a 
ship at a range of 2000 yards, from a site 100 feet above sea level. 
Here the tangent of the angle of sight is Ad which gives the angle as 
1° roughly, and the angle of descent at 2000 yards given in the range 
table is 2° 43', making the whole angle of descent nearly 4°. Taking 
it as 4° we get the horizontal distance corresponding to this, with a 
height of 14 feet, as nearly 70 yards. To this we may add at least a 
