ea.

[Illustration: FIG. 3.--Diagram showing principal characteristics of a
coastal motor boat (C.M.B.). Speed 50 miles per hour. _A._ Hydroplane
hull, so constructed as to rise on to surface when travelling at full
speed. _B._ Covered wheel-house. _C._ Navigating well. _D._ Wireless
aerials. _E._ Depth charges (2 small size). _F._ Manhole to
engine-room.]

There were three types of C.M.B.'s. One had a length of only 44 feet,
and was intended for carriage on the decks of light cruisers or other
moderate-sized surface ships. The armament was a Lewis machine gun and
two depth charges for anti-submarine warfare. The next class were 55
feet in length and operated from coast bases. These were fitted with one
or more Whitehead torpedoes, launched by an ingenious contrivance from
the stern. Class III. were 70 feet in length, and were commissioned just
before the signing of the Armistice. They were fitted for mine-laying
close up to enemy harbours.

[Illustration: FIG. 4.--Plan of coastal motor boat, showing torpedo in
cleft stern. _A._ Whale-back or arched deck. _B._ Wheel-house. _C._
Navigating well. _D._ Engine-room. _E._ Foreward petrol tanks. _F._
Forepeak. _G._ Depth charges. _H._ Cleft stern with torpedo ready for
launching. _I._ Whitehead torpedo, launched stern first.]

The maximum speed of the 55-feet C.M.B.'s, which were the most numerous,
was 40 knots, or nearly a mile a minute. They were driven by twin screws
coupled to twin engines of 350 h.p. each--working at 1350 revolutions
per minute. Being of very shallow draught, some 26 inches, these little
vessels could skim, hydroplane fashion, over any ordinary mine-field,
and a torpedo fired at them would merely pass under their keel. The risk
of destruction from shell-fire was also reduced to a minimum by their
small size and great speed. Their principal enemies were, however,
seaplanes armed with machine guns.

[Illustration: A 40-FT. COASTAL MOTOR BOAT TRAVELLING AT FULL SPEED

_Thornycroft & Co., Ltd._]

[Illustration: A 40-FT. COASTAL MOTOR BOAT TRAVELLING AT FULL SPEED

_Thornycroft & Co., Ltd._]

It is not difficult to imagine a fight between a C.M.B. travelling at 40
knots, firing with its little Lewis gun at a big seaplane swooping down
from the clouds at the rate of 70 miles an hour, and splashing the water
around the frail little grey-hulled scooter with bullets from its
machine gun. This actually occurred many times off the Belgian coast,
and is a