rtment in
which the driver and his helper are perched high above the ground to
direct the movements of the huge steel beast.

In the middle is the ammunition room from which the guns carried in the
two side turrets are fed. At the rear is the engine room. From two or
four gasoline engines are used--these driving the rear axle and its
integral sprockets over which the caterpillars run. The latter run an
idler pulley or sprockets at the extreme front ends and are supported by
means of rollers attached to the upper portion of the frame on each side
when passing over the top. This movement of the caterpillar belts is
exactly analogous to that of the ordinary variety of garden insect with
the same name which similarly lays down his own track by humping his
back continuously and regardless of the land surface.

The tanks are steered by a pair of small ordinary wheels at the rear.
These are supported in a pivot on a frame extended from the rear. They
are merely for steering, and support none of the weight of the tank
except when bridging wide trenches or dips in the surface. Steering can
be accomplished by making one caterpillar go faster than the other by
manipulating clutches on the driving mechanism.

TANK'S "CATERPILLAR" FEATURE.

The "caterpillar" feature of the tank had its origin in the caterpillar
belts or shoes which were first used on the great field guns and
mortars--those tremendous weapons which shoot bombs and shells weighing
tons and containing 500 or more pounds of guncotton or explosive which
on contact is discharged, rending everything for yards around.

These guns, as well as the smaller field guns, have had attached to them
great shields of steel behind which the gunners stand, so that they are
protected against the old-fashioned sharpshooters whose duty it was to
pick off the gunners.

The caterpillar or wheel belts on the big guns consist of flat blocks,
or shoes, wider than the tires of the wheels. They are hinged and
fastened together so as to form a great chain, and when placed on the
wheels present broad surfaces to the ground and keep the gun carriages
from sinking into the soft earth. With a set of these shoes a heavy gun
can be drawn over soft and irregular ground, which would be almost
impassable where the gun is mounted on wheels of ordinary width.

Before these belts were devised it was necessary for every gun crew to
carry a supply of beams, jackscrews and devices to be used in
extric