The 240-millimeter howitzer mounts were of two types--one following closely the St. Chamond type of the French and the other being a self-contained unit designed by Ordnance Department engineers. The self-contained type is a single unit that mounts both the power plant and the howitzer and for which it is necessary to provide additional cargo-carrying caterpillars to haul ammunition and fuel. Two units make up the St. Chamond type. One mounts the gun and electric motors; the other, a limber, mounts the power plant and carries ammunition. In the battle area the St. Chamond type had the peculiar advantage that the power-plant unit could be run to shelter and be available for a rapid advance or change of location of the gun mount as the situation might demand. With the self-contained unit a direct hit by the enemy would put both gun and power plant out of commission. Contracts for the caterpillar mounts called for the completion of the entire program not later than February, 1919. All the firms engaged on the work of production were putting forth every effort when the armistice was signed and there was every reason to believe deliveries would be as scheduled. The termination of hostilities caused all contracts to be reduced. Provisions have been made for only enough caterpillars of each type to provide for further experimental work. Twenty mounts equipped with caterpillar treads and mounting 7-inch Navy rifles were built by the Baldwin Locomotive Co. for the Navy Department. These were so successfully operated that orders were placed for 36 similar units for the use of the Army, but since the signing of the armistice this order has been cut to 18. The great gun on a caterpillar mount fires its death-dealing projectile, and almost before the shot has reached its destination the caterpillar mount has moved the gun to another point. With motor still running the gun is fired again and once more quickly moved on to another location, so that the enemy's artillery is unable to get its range. [Illustration: TEN-TON ARTILLERY TRACTOR.] [Illustration: FIFTEEN-TON ARTILLERY TRACTOR.] [Illustration: TWO AND ONE-HALF TON ARTILLERY TRACTOR.] [Illustration: FIVE-TON ARTILLERY TRACTOR.] [Illustration: 20-TON ARTILLERY TRACTOR.] [Illustration: STAFF OBSERVATION CAR. Special body for field touring on a White one-ton truck chassis.] [Illustration: RECONNAISSANCE CAR ON WHITE CHASSIS. The machine-gun truck is similar except for the addition of gun racks under rear seat and on Commerce chassis.] [Illustration: CATERPILLAR TRACTOR WITH 3-INCH GUN MOUNTED ON IT.] [Illustration: ANOTHER VIEW OF CATERPILLAR TRACTOR WITH 3-INCH GUN.] [Illustration: CATERPILLAR TRACTOR MOUNTING AN 8-INCH HOWITZER WHICH HAS A RANGE OF 6 MILES WITH A PROJECTILE WEIGHING 200 POUNDS.] [Illustration: LIGHT REPAIR TRUCK ON DODGE CHASSIS. Special body with tools for making minor motor repairs.] [Illustration: THREE-INCH FIELD GUN TRAILER.