er of lights, both guns and lights
increasing at some places nearly fourfold. But even with the best
possible arrangement of this form of defence, the possibility of
interference by fog, mist or rain introduces a considerable element of
uncertainty.

About the same time, and largely on account of the demand for better and
quicker firing, the "automatic sight" was introduced (see ORDNANCE:
_GARRISON_; and SIGHTS). In this, a development of the principle of the
position-finder, the act of bringing an object into the field of the
auto-sight automatically lays the gun. In order to take full advantage
of this, the ammunition was made up into a cartridge with powder and
shell in one case to allow of the quickest possible loading. It may be
added that the efficiency of the auto-sight depends on the gun being a
certain height above the water, and that therefore the rise and fall of
tide has to be allowed for in setting the sight.

In view of the possible interference by fog it was thought wise at an
early stage to provide, towards the rear of the defences, some form of
physical obstacle behind which ships could lie in safety. Such an
obstacle had been designed in the early days by the Royal Engineers and
took the form of a "boom" of baulks of timber secured by chains. Such
booms were limited in size by considerations of expense and were only
partially successful. About 1892 the British navy took the matter up and
began experiments on a larger scale, substituting wire hawsers for
chains and using old gunboats to divide the booms up into sections of
convenient length. The result was that booms were definitely adopted as
an adjunct of coast defence. Their place is behind the lighted area, but
within reach of some of the anti-torpedo boat batteries.

Other forms of obstacle to torpedo boat attack, based on a modification
of contact mines or a combination of mines and passive obstructions,
have been tried but never definitely adopted, though some form of
under-water defence of this description seems necessary to meet attack
by submarines.

We may now summarize the anti-torpedo boat defences. These are, first,
an outpost or look-out line of electric search-lights, then a main
lighted area composed of fixed lights with which there are a
considerable number of 12-pounder or 4-in. Q.F. guns fitted with
auto-sights, and behind all this, usually at the narrowest part of the
entrance, the boom.

Once coast defences are designed and i