There were, of course, units from the United States, French, Japanese, Italian and Brazilian navies, in addition to the formidable British armada.
The auxiliary units were all based on one or other of the fifty odd war stations which encompassed not only the coasts of Great Britain and Ireland, but also the littoral of every land in our world-wide Empire. The numbers given here do not include the local fleets of purely colonial naval bases, nor the large flotillas of destroyers and "P" boats operating in home and foreign waters in conjunction with the auxiliary navy. If these were incorporated the anti-submarine fleets would be almost doubled.
Now that the reader is familiar with the raison d'être of the new navy, the personnel, the ships and their formation into fleets, the scope and limitations of their activity, and of the losses they sustained, the way is clear for a description of the curious weapons used, the mysteries of anti-submarine warfare, and the bases themselves before entering the zone of war and seeing something of the actual work of the auxiliary navy.
CHAPTER V
THE HYDROPHONE AND THE DEPTH CHARGE
Of all the weapons used in the anti-submarine war the two most important were the hydrophone and the depth charge. They were employed in conjunction with each other and comprised the surface warship's principal means of offence against submarines operating beneath the surface.
The hydrophone resembles a delicate telephone. It is so constructed that when the instrument is lowered over the side of a ship into the sea any noise, such as the movement of a submarine's propellers, can be heard on deck by an operator listening at an ordinary telephone receiver connected to the submerged microphone by an electrified wire.
There were many different types of hydrophone in use during the Great War. So important was this instrument for the work of submarine hunting that money was spent in millions, and a corps of naval and civil experts were engaged for several years, bringing it to a state of efficiency. Each type introduced into the Service was an improvement on its predecessor, and there were different patterns for the use of almost each class of vessel. The fast destroyer required a different instrument to the slow-moving trawler. The motor launch could only employ successfully a totally different type to the submarine, and, to add to the difficulties, the German submarines themselves were generously supplied with similar instruments. The games of "hide-and-seek" played on and under the seas with the aid of this wonderful little instrument would have been distinctly amusing had men's lives—and often those of women and children—not been dependent upon the issue.