With such a system of revictualling, submarines should be able to operate secretly for long periods and virtually hold to the sea during the entire time, doing in that interval what would be absolutely impossible for any type of surface fighting craft of kindred displacement and military power. The submarine commander would be the only one having knowledge of the position of his submerged supply bases, and he could place them under cover of night just where they would contribute best to the carrying out of the operations planned for him. [Illustration: SUBMARINE "SEAL"--LAKE TYPE U. S. This vessel is unique in that she was the first vessel built that was provided with deck torpedo tubes that could be trained and fired to either broadside when the vessel is submerged, in addition to the vessel's hull tubes. In her acceptance trials her crew took her down to a depth of 256 ft. She broke the record for speed in the U. S. Navy.] On almost every coast there are areas where submarines could sink safely to the bottom in moderate depths of water, and there are also quiet coves but little frequented where ideal resting places could be found for the submerged supply boats. With these failing, however, the tenders could be sunk to the water-bed in the open sea, and with their bottom wheels to rest on, working upon pneumatic buffers, they need not feel any vertical motion of the sea even in the stormiest weather. I have found that such motion actually exists forty feet and more below the surface when the ground swell is deep. [Illustration: BRITISH SUBMARINE B-1 (HOLLAND TYPE) A sister ship to B-11, that sank the Turkish battleship "Messudieh" in the Dardanelles.] Of course, the submarine must rise to the surface from time to time in order to draw in fresh air to fill her pressure tanks and also to recharge her storage batteries. The electrical accumulators are charged by means of the oil motors, and these engines are so greedy for air that they must have the free atmosphere to draw upon when working. Therefore the submarine would rise to the surface to perform these services during the night time, and boats seeking submarines after dark have a task cut out for them pretty much like that of hunting for the proverbial needle in a haystack. If the commander of a submarine recognizes that the first principle of successful submarine raiding is never to betray his position by exposing his periscope while under way when within sight of the enemy, his vessel becomes invulnerable, because it is an invisible object. The submarine vessel is then invincible, because all the science of naval architecture has not been able thus far to devise a protection against the mine and torpedo. CHAPTER VI THE POSSIBILITY OF DEFEATING THE SUBMARINE