June 5, 1915. 
LAND AND .WATER. 
temporary navies, and so placed himself, at the 
normal finish of his career, in a category by him- 
self, so is Sir Henry Jackson a type of ofiicer the 
times most clamorously demand — a man who can 
bring to the administration of the Na\y a mastery 
of its technical problems that is quite unparal- 
leled, and broadened and illumined by a con- 
tinuous study of its higher strategics. The 
new administration is being put to an im- 
mediate and most severe test. But whatever 
losses and set-backs there may be — and both are 
to be expected — Mr. Balfour and Sir Henry Jack- 
son can be looked to with absolute confidence to 
handle the situation with the coolness, the 
courage, the judgment, and the knowledge that it 
requires. 
THE CRUX OF NAVAL GUNNERY. 
IF two skips are stationary at any distance apart, the range 
remains constant; if both advance in the same direction 
and at the same speed, the range remains constant. B'lt 
if either mancruvres, the range reflects the difference of 
movement. Suppose a ship advances in a straight line 
towards a fixed target at an even speed, the range 
must decrease at that speed; such a manoeuvre would 
represent no difficulties to gunnery. The sights would 
bimply be lowered at the rate at which the ship was moving. 
If ?he was going 12 knots, at 400 yards a minute; at 15 knots, 
500 yards a minute, and so on. Given a reliable speedometer, 
good communications, and an efficient sight-setting service, 
it would be exactly as if the ship was stationary. 
But if the ship went on a course not directly towards or 
away from the target, the rate at which the range altered 
would not be constant — it would vary. As the range in- 
cieased, the change in each successive minute would become 
less — as it diminished the change would become greater. On 
the other hand, the rate would change very little and very 
slowly. If the target were visible, with the instriui«'nta 
generally in use, this changing rate could be ascertained; 
and if the speed of the ship was not very high, the fights 
«ould still be correctly altered. 
If the firing ship, however, began to manoeuAre — that 
rest or on parallel courses; or changing, when either moves 
differently from the other. Next, that the rate at which 
the range changes is either constant — which is rare, because 
limited to movement in certain fixed relative directions — or 
varying. Finally, that the variations of the rate reflect the 
manoeuvres of the ship. If the ship is going slow and 
changes her course only by small turns — a few degrees at a 
time — then the variations in the rate will be small ; while if 
the ship is fast and makes large turns, the variation will be 
large. As we have seen in a given case with a fixed target, a 
turn of 90 degrees, made in 90 seconds, can convert a de- 
creasing rate of 500 yards into an increasing rate of a like 
amount — a total change in rate of no less than 1,000 yards a 
minute and a half ! 
How can the range be kept in such conditions ? Ob- 
viously, the only way would be to make the sights move aa 
the range changes. It all turns on continuous knowledge of 
the rate, or, rather, on the rate being anticipated and con- 
tinuouslg controlling the sights. 
The rate-finding instruments used in most navies are 
based upon a formula that was first embodied in an instru- 
ment made and patented, some ten or eleven years ago, by 
Captain Duniaresq, of the Royal Navy. This instrument, 
when set to the firing ship's speed and to the speed and 
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is, make sudden and large turns — then the range would jump 
up and down. Suppose, for instance, a ship was advancing 
at a high speed with a target bearing 45 degrees from the 
port bow — that is, before the beam — and suddenly turnml 
90 degrees to starboard. If before the turn the range was 
decreasing at 500 yards a minute, it would now be increasing 
at practically the same rate. The turn, therefore, would have 
converted a decreasing rate into an increasing rate. 
The reader will have perceived from the foregoing thab 
ranges are either constant — when the ship and target are at 
course of the target if the target is moving, must first be 
held in such a position on board ship that its zero line is in 
coincidence with that of the firing ship's course — no easy 
matter when a ship is yawing, and almost impossible if the 
ship is turning. A pointer has then to be directed at the 
target. When all this is done, the rate at which the range 
is changing at that moment is indicated. Messrs. Barr and 
Stroud have introduced an improved instrument, which is, 
in fact, a mechanical equivalent to Captain Duniaresq 's in- 
dicator. It shows the rate on a dial instead of on -a table. 
11* 
