f Forth for the benefit of the
battle cruisers, and outside Harwich for Admiral Tyrwhitt's light
forces.

[Illustration: MODEL OF A COASTAL MOTOR BOAT (55 FT.) WITH TORPEDO AND
FOUR DEPTH CHARGES

_Thornycroft & Co., Ltd._]

A passage known as the "war channel"--about which more will be said
later--extending from the Downs to Newcastle, was swept daily by relays
of sweepers operating from the anti-submarine bases along this 320 miles
of coast-line. This buoyed and guarded channel formed a line of supply
for the great fleets in the north.

Each big fighting formation was provided with a special flotilla of fast
fleet sweepers, which were capable of clearing the seas ahead of the
battleships and cruisers moving at 20 knots. This was a separate
organisation to what may be described as the routine sweeping of the
trade routes. These vessels were always within call of the fleets they
served.

It has been estimated that over 1000 square miles of sea were swept
daily by the anti-mine fleets of the British navy during the four years
of war. This may not sound a very stupendous figure compared with the
area of the danger zone, but in practice it necessitated terribly hard
work from dawn to dusk by several thousand ships and many thousands of
men in summer heat and winter snow.

There was in addition to all this the clearing of British mine-fields no
longer required in the positions in which they had been originally laid.
This was not entirely an after-the-war problem, for although the
great mine barriers were left until peace was assured, there were fields
of minor importance which had to be cleared to meet new situations as
the years of war passed swiftly by. A notable instance of this was the
destruction of a big field of some 400 mines off the Moray Firth.

The foregoing refers only to the minesweeping in the principal danger
zones in British waters, no account being taken of the work carried out
by Allied vessels in the Mediterranean, off the coasts of France, Italy,
Greece, Gallipoli, and in such distant seas as those washing the shores
of New Zealand, Australia, Hong-Kong, Japan, Singapore, Bombay, Aden,
the Cape of Good Hope, the United States, Eastern Canada, West Africa
and Arctic Russia, in all of which mines were laid by surface raiders
like the _Wolfe_, and afterwards located and cleared by Allied warships.

From the foregoing some idea of the gigantic nature of the task will be
obtained, and we can pass on