hes, are weakest in
shell-power, but they possess a mobility greater than any other
artillery and can be moved in country which would present insuperable
obstacles to wheeled traffic. _Pack Howitzers_, with a calibre of 3.7
inches, are particularly valuable in close country, the high angle of
descent enabling the attack or defence to search the steepest cover.
_Horse Artillery Guns_, firing a 13-pound shell, are the most mobile of
all wheeled artillery and are normally employed with mounted troops.
All ranks of the Royal Horse Artillery are mounted, and its mobility is
scarcely less than that of cavalry. _Field Guns_, with a calibre of 3
inches, firing an 18-pound shell, are the principal artillery weapon of
a field army. Although inferior in mobility to Pack or Horse
Artillery, they have greater shell-power and afford the principal
support to infantry in closing with or repelling the enemy. Their
power to inflict casualties {171} by enfilade fire with shrapnel makes
them specially suitable in the defence, and the accuracy of modern
weapons enables them to co-operate in the Attack with covering fire,
under the protection of which infantry may advance unimpeded to the
assault. In addition to their normal functions, and to their
employment in counter-battery work, they can be employed in the
reduction of defences by bombardment with High Explosive shells, in
neutralising an area by the use of gas shells, or in providing
artificial cover by the production of _Smoke_. _Field Howitzers_, with
a calibre of 4.5 inches, have increased offensive power and practically
the same mobility as field guns.

Light guns are the principal weapons for protection against _Aircraft_
and for defence against _Tanks_. The Tank is powerless against
artillery, and its most effective enemy is light artillery. During the
_First Battle of the Somme_ a new terror was added to the British
attack by the introduction of the Tank, which surmounted inequalities
in the ground, crushed the wire defences, and crossed the trenches.
Although accompanied by infantry, it was regarded as an all-conquering
and decisive factor. At one period of the battle, however, a number of
Tanks were placed out of action by a single field gun, manned and fired
with the greatest gallantry by a single German artillery officer, who
fired point-blank at each Tank as it surmounted the crest of a rise.
Infantry were in close support, and a single Lewis-gun section could
hav