Submarine detection is done by sound. No one has yet produced a noiseless engine, and when a boat is moving submerged, even at her slowest speed, the noises inside her are carried through the water to a considerable distance.
Tested in Mediterranean Detectors indicate to within a few yards their exact point of origin. The gear was used effectively at the time of the 1935 crisis in the Mediterranean, when Italian submarines were located as they were patrolling off Malta, and forced to the surface by destroyers.
The submarine in future will be completely useless against ships of the fighting fleet—it did not do much damage to them in the last war—and convoys of freighters protected by the new escort vessels are not likely to lose one ship in a hundred.
Text read from the printed page and cleaned; old type leaves the occasional error.