The ordnance bureau of the navy developed a new type of mobile mount for heavy guns which, by the use of caterpillar belts, made them as mobile as field artillery although the weight and muzzle velocity of the huge projectile rendered impossible the use of a wheeled gun carriage. The entire gun and mount, weighing 38 tons, can be readily transported by this means over any kind of ground. Immense naval guns, originally intended for use on battle cruisers, were sent to France with railway mounts especially built for them by the navy. Their important and successful operations overseas are described in the chapter on “The Navy on Land.” Smoke producing apparatus, to enable a ship to conceal herself in a cloud of smoke, was evolved of several kinds, for use by different types of vessels. A shell that would not ricochet on striking the water, when fired at a submarine, and so glance harmlessly away in another direction, was an immediate necessity, brought about by the conditions of sea warfare. After many experiments a shell was devised that on striking would cleave the water, to the menace of the submarine’s hull, and, equipped with a depth charge, was soon in quantity production. A heavy aeroplane bomb which united the qualities of a bomb with those of a depth charge and did not explode on striking the water was another development of the navy ordnance bureau, which also devised a nonrecoil aircraft gun which, after much experiment, was installed on our seaplanes and put into quantity production. Its success meant the passing of an important milestone in aircraft armament. An American device for detecting the sounds made by a submarine gave highly important aid to that phase of the war. The Navy Department equipped our own submarines, destroyers and chasers with them and furnished them in large numbers to the British navy.