At just what period of the war the Germans woke up to the vital importance to them of an enormous submarine fleet is not known. It may have been immediately upon the amazing exploit of Captain Weddigen in the North Sea. At any rate the war had not long progressed before the destruction caused by German submarine attacks began to awaken the apprehension of the Allies and neutral nations. Retaliation in kind was impossible. The Germans had neither merchant nor naval ships at sea to be sunk. The rapidity with which the volume of the loss inflicted upon merchant shipping grew indicated an equally rapid increase in the size of the German underwater fleet. Neutrals were enraged by the extension by the Germans of the areas of sea in which they claimed the right to sink neutral ships, and their growing disregard for the restraining principles of international law. How greatly they developed the submarine idea was shown by their construction in 1916 of vessels with a displacement of 2400 tons; a length of 279 feet, and a beam of 26 feet; a surface speed of 22 knots, cruising radius of 6500 miles, mounting 4 to 8 guns and carrying a crew of from 40 to 60. But it was reported that two vessels designed primarily for surface cruising, but nevertheless submersible at will, had been laid down of 5000 tons, a length of 414 feet, and a radius of 18,000 to 20,000 miles. These "submersible cruisers" as they were called, mounted 6 to 8 guns, 30 torpedo tubes, and carried 90 torpedoes. What part vessels of this type shall play in war is still to be determined.
Of the smaller naval powers, Italy comparatively early had become interested in the building of submarines. Most of her boats are of the Laurenti type--which is a very close adaptation of the Lake type. Russia and Japan, especially the latter, built up fairly efficient underwater fleets. The lesser countries, like Austria, Holland, Sweden, Denmark, Norway, and Spain have concerned themselves seriously with the creation of submarine fleets. The submarine boats of all of these countries in most instances were either of the Lake or Holland type though frequently they were built from plans of English, French or German adaptations rather than in accordance with the original American plans.
The exact number of submarines possessed now by the various navies of the world is a matter of rather indefinite knowledge. Great secrecy has been maintained by every country in this respect. From a variety of sources, however, it has been possible to compile the following list which at least gives an approximate idea of the respective strength of the various submarine fleets at the beginning of the war. The numbers assigned to each country are only approximate, however, and include both boats then in existence or ordered built: United States 57; Great Britain 104; France 92; Germany 36; Italy 28; Russia 40; Japan 15; Austria 12; Holland 13; Denmark 15; Sweden 13; Norway 4; Greece 2; Turkey 2; Brazil 3; Peru 2.
Having traced the development of the submarine from its earliest beginnings to recent times we are naturally now confronted with the question "What are the principal requirements and characteristics of the modern submarine?"
The submarine boat of to-day, in order to do its work promptly and efficiently, must first of all possess seaworthiness. This means that no matter whether the sea is quiet or rough the submarine must be able to execute its operations with a fair degree of accuracy and promptness and must also be capable of making continuous headway. Surface and underwater navigation must be possible with equal facility and it is necessary that a state of submergence can be reached without loss of time and without any degree of danger to the boat's safety. At all times, travelling above water or below, the submarine must possess mechanical means which will make it possible to control its evolutions under all conditions. Furthermore, the ability of the submarine to find and to observe objects in its vicinity must not be greatly reduced when it is in a submerged position. In the latter it also becomes of extreme importance that the provisions for ventilation are such that the crew of the submarine should lose as little as possible in its efficiency and comfort. A fair amount of speed both on and below the surface of the water is essential and the maintenance of the speed for a fairly long period of time must be assured.
