Around each outer edge runs an endless belt of steel
plates, hinged together, with ridges at the joints, and
these broad belts of steel plates, like the platforms of
some moving stairways used in department stores, moving
around, give motion to the tank.

Inside, well protected from the fire of enemy guns by
steel plates, are the engines for driving the belts, or
caterpillar wheels, as they are called. There is also the
steering apparatus, and the guns that fire on the enemy.
There are cramped living and sleeping quarters for the
tank's crew, more limited than those of a submarine.

The tank is ponderous, the smallest of them, which were
those first constructed, weighing forty-two tons, or about
as much as a good-sized railroad freight car. And it is this
ponderosity, with its slow but resistless movement, that
gives the tank its power.

The tank, by means of the endless belts of steel plates,
can travel over the roughest country. It can butt into a
tree, a stone wall, or a house, knock over the obstruction,
mount it, crawl over it, and slide down into a hole on the
other side and crawl out again, on the level, or at an
angle. Even if overturned, the tanks can sometimes right
themselves and keep on. At the rear are trailer wheels,
partly used in steering and partly for reaching over gaps or
getting out of holes. The tanks can turn in their own
length, by moving one belt in one direction and the other