odern
campaign the opposing armies tend to become immobile, chiefly owing to
the great power conferred on the defence by modern armaments. The
armies will then be distributed in great depth, and the attackers are
faced with the necessity of breaking through not one position only, but
a series of positions, extending back to a depth of several miles"
("Infantry Training, 1921").

Penetration, followed by the sundering of the Franco-British Armies,
was clearly the intention of the German {52} High Command in the
_Second Battle of the Somme_, which opened on March 21, 1918. The
German Armies had entrenched themselves after the First Battle of the
Marne (September, 1914), and for 43 months had been confronted by the
Allied Nations of Britain, France, and Belgium, reinforced at the close
by Portuguese troops and by the National Army of the United States.

Within the investing lines of the Western Front the German Armies were
besieged, the barrier reaching from the Belgian coast to the frontier
of Switzerland, while the armies of Austria-Hungary were similarly
penned in by the army of Italy, from Switzerland to the Adriatic. The
internal collapse of Russia, in 1917, enabled von Hindenburg to assume
the offensive, with upwards of 1,500,000 men released from the Eastern
Front, and part of this reserve power was projected, with the
Austro-Hungarian Armies, in a fierce attack on the Italian lines. The
success of this manoeuvre continued until reinforcements were
dispatched from other parts of the Allied lines, and a diversion in the
region of Cambrai by the British III. Army, under Sir Julian Byng
(November 20, 1917), prevented the dispatch of further German reserve
power to the Italian Front, and necessitated a counter-thrust in
France. The battlefields of France again resumed their importance as
the vital point in the theatre of operations, and in the spring of
1918, profiting by the improved positions and prospects in the West,
Ludendorff attempted to break through the investing lines on a 50-mile
front. The attack was heralded by a terrific bombardment, and
culminated in a desperate thrust against the British Armies north and
south of the River Somme, the points of penetration aimed at being the
British right, where it was linked up with the French on the River
Oise, in the neighbourhood of La Fere, and the British line of
communications in the neighbourhood of Amiens. The whole British line
opposite the thrust was h