limited areas of water by patrols, nets, etc., than it would be to protect the entire trans-oceanic length of the steamship lanes. If the submersible were capable of dealing directly with the destroyer in gun-fighting, a tremendous revolution would take place in the tactics of "submarine swatting." Then it would be difficult to see how the submersible could be dealt with.

Improvement in motive machinery is the vital necessity in the development of the submersible. The next few years may see unexpected strides taken in this direction. A great deal will also be accomplished in perfecting methods of receiving sounds under water, particularly in relation to ascertaining the direction of these sounds. When this is done, it will be possible for the submersible commander to tell a great deal about the positions of the vessels above him, and thus his artificial ears will compensate to a great extent for his blindness. By the addition of a greater number of torpedo-tubes, and the improvement of their centralized control in the hand of the commander at the periscope, along lines which we are now developing, it will be possible for the submersible to achieve a greater effectiveness in its torpedo fire. Probably torpedoes will then be used only against the more important enemy units, such as battleships, cruisers, and the like. To be certain of striking these valuable targets would be worth expending a number of torpedoes in salvo fire.

Whether the German U-boat campaign succeeds or not will be largely a question of the number of submersibles that the Central Powers can put into service, and to what extent the submersible will be developed during the present war.

III

German submarines have sunk over 7,250,000 tons of the Allied shipping. In December, 1916, it was stated in the British Parliament that the merchant marine of Great Britain had at that time over 20,000,000 tons. Within the first three months of the unrestricted submarine warfare, 1,100,000 tons of British shipping went to the bottom. At this rate, England would lose 25 per cent of her merchant marine per annum. It is for this reason that the attention of the entire world is concentrated upon the vital problem of the submarine menace. On land, the Central Powers are still holding their ground, but there is a continuous increase of the forces of the Allies which should lead finally to such a preponderance of power as will overwhelm the forces opposed to them. The Allied armies, however, depend for their sustenance and supplies upon the freedom of the seas. The trade routes of the world constitute the arteries which feed the muscles of these armies. Germany is endeavoring to cut these arteries by the submarine. Should she even appreciably limit the supplies that cross the ocean to the Allies, she will bring about a condition that will make it impossible to augment their armies. In this way there will inevitably be a deadlock, which, from the German standpoint, would be a highly desirable consummation.

Obviously, the first method of handling the submarine problem would be to bottle the German undersea craft in their bases. There has been a number of proposals as to how best to accomplish this. It has been stated that the English Navy has planted mines in channels leading from Zeebrugge and other submarine bases; but it is necessary only to recall the exploits of the E-11 and the E-14 of the British Navy at the Dardanelles, to see that it would not be impossible for the Germans to pass in their U-boats through these mine-fields into the open sea. It will be remembered that the E-11 and the E-14 passed through five or more mine-fields, thence through the Dardanelles into the Sea of Marmora, and even into the Bosphorus under seemingly impossible conditions. Yet, in spite of the tremendous risks that they ran, these boats continued their operations for some time, passing up as far as Constantinople, actually shelling the city, sinking transports, and accomplishing other feats which have been graphically described in the stories of Rudyard Kipling. And again, if the mine-fields were placed in close proximity to their bases, it would be comparatively easy for German submersibles of the Lake type, possessing appliances to enable divers to pass outboard when the vessel is submerged, to go out and cut away the mines and thus render them ineffective.

Nets are also used to hinder the outward passage of the submarine. These nets can likewise be attacked and easily cut by devices with which modern U-boats are equipped. The problem of placing these obstacles is a difficult one, in view of the fact that the ships so engaged are harassed by German destroyers and other enemy craft. Outside of Zeebrugge, shallow water extends to a distance of about five miles from the coast, and it has been suggested that a large number of aircraft, carrying bombs and torpedoes, should be used to patrol systematically the channel leading from that port to deep water, with the intent of attacking the submersibles as they emerge from this base. It is ridiculous to suppose that the Germans would not be able to concentrate an equally large number of aircraft, to be supported also by anti-aircraft guns on the decks of destroyers and by the coast defenses. We have not yet won the supremacy of the air, and it must inevitably be misleading to base any proposition on the assumption that we are masters of that element.

The problem of bottling up the submersibles is enormously difficult, because it necessitates operations in the enemy's territory, where he would possess the superiority of power. I believe that the question of operations against the submarine bases is not a naval but a military one, and one which would be best solved by the advance of the Western left flank of the Allied armies.

The second method is to attack the submarines with every appliance that science can produce. In order to attack the submarine directly with any weapon, it is necessary first to locate it. This is a problem presenting the greatest difficulty, for it is by their elusiveness that the submarines have gained such importance in their war on trade. They attack the more or less helpless merchant ships, and vanish before the armed patrols appear on the scene.

Almost every suitable appliance known to physics has been proposed for the solution of the problem of submarine location and detection. As the submarine is a huge vessel built of metal, it might be supposed that such a contrivance as the Hughes induction balance might be employed to locate it. The Hughes balance is a device which is extremely sensitive to the presence of minute metallic masses in relatively close proximity to certain parts of the apparatus. Unfortunately, on account of the presence of the saline sea-water, the submersible is practically shielded by a conducting medium in which are set up eddy currents. Although the sea-water may lack somewhat in conductivity, it compensates for this by its volume. For this reason, the induction balance has proved a failure.

But another method of detecting the position of a metallic mass is by the use of the magnetometer. This device operates on the principle of magnetic attraction, and in laboratories on stable foundations it is extremely sensitive. But the instability of the ship on which it would be necessary to carry this instrument would render it impossible to obtain a sufficient degree of sensitiveness in the apparatus