ade of the element of
surprise. Large masses of men were brought up near the front by night
marches, and in daytime were hidden from airplane observation by smoke
screens, camouflage of various kinds, and by the shelter of woodlands.
In this way any portion of the opposing trench line could be subjected
to a heavy, unexpected attack.

Secondly, the advance was prepared for by the use of big guns in
enormous quantities and in new ways. The number of guns brought into use
in this offensive far exceeded that put into the Verdun offensive of
1916, which had been looked upon as the extreme of possible
concentration of artillery. The shell fire was now to be directed not
only against the trenches, but also far to the rear of the Allied
positions. This would break up roads, railways, and bridges for many
miles behind the trenches and prevent the sending of reinforcements up
to the front. Vast numbers of large shells containing poisonous
"mustard" gas were collected. These were to be fired from heavy guns and
made to explode far behind the Allied lines. By this means suffocation
might be spread among the reserves, among motor drivers, and even among
the army mules, and by deranging the transport service make it
impossible to concentrate troops to withstand the German advance.

In the third place, "shock" troops composed of selected men from all
divisions of the army, were to advance after the bombardment, in a
series of "waves." When the first wave had reached the limit of its
strength and endurance, it was to be followed up by a second mass of
fresh troops, and this by a third, and so on until the Allies' defense
was completely broken.

By their excess in numbers and by these newly devised methods of warfare
the German leaders hoped to accomplish three things: (1) to separate the
British army from the French army; (2) to seize the Channel ports and
interrupt by submarines and big guns the transportation of men and
supplies from England to France; and (3) to capture Paris and compel the
French to withdraw from the war. Let us now see how and why the Germans
failed to secure any one of these three objectives, and how the Allied
forces resumed the offensive in the summer of 1918.

THE GERMAN ADVANCE.--Five great drives, conducted according to the
newly devised methods of warfare, were launched by the Germans between
March 21 and July 15, 1918. The first, continuing from March 21 to April
1, called the battle of Picardy, was d