Even in the Russo-Japanese war, where the mine was little used, it exerted a marked influence on the course of the war; the Germans based their hopes of victory in the early days of the struggle entirely on a war of attrition, waged against men-of-war, as well as merchant ships.

The submarine, which was thrown into the struggle in increasing numbers, represented an entirely new development, for the submarine is a vessel which can travel unseen beneath the water and, while still unseen, except for a possible momentary glimpse of a few inches of periscope, can launch a torpedo at long or short range and with deadly accuracy.

In these circumstances it became imperative to organize the Admiralty administration to meet new needs, and to press into the service of the central administration a large number of officers charged with the sole duty of studying the new forms of warfare which the enemy had adopted and of evolving with scientific assistance novel methods of defeating his tactics.
Whilst the enemy's campaign against merchant shipping always gave rise to anxiety, there were certain periods of greatly increased activity.
During the summer months of 1916 the losses from submarine attack and from submarine-laid mines were comparatively slight, and, in fact, less than during the latter half of 1915, but in the autumn of 1916 they assumed very serious proportions.

This will be seen by reference to the following table, which gives the monthly losses in British, neutral and Allied mercantile gross tonnage from submarine and mine attack _alone_ for the months of May to November inclusive: May ...

122,793 June ...