=Echo and Magnetic Devices.=--Locating submarines by echo has been proposed, but apparently without thought as to what would happen to the vessel giving out the sound in the effort to get an echo back from a submerged submarine, lying in wait with her "ears" waiting to hear some suspicious sound. Also, magnetic devices for the purpose of detecting submarines, if ever found practical, will probably be kept so busy leading their operators to and investigating large steel ships that have already been sunk by submarines that they will probably miss the little submarine, which can easily sink them while they are investigating these other sunken ships. =Channel and Open-sea Nets.=--These have been and are being used with some success, but that success has been attained only because at the beginning of the war the submarines had no means for determining the presence of the nets before becoming entangled in their meshes, and when they once became entangled they had no means to cut themselves loose. Devices are now available which enable the commander of a submarine to locate a net before reaching it, and to destroy that net and all its attached mines with but little danger to his own vessel. To what extent these devices are being used is unknown. However, when the submarine is not especially fitted for the detection and destruction of nets and attached mines, they are probably the most efficient type of trap yet provided for capturing and destroying these "submarine devil fish." The _Scientific American_ published an article by me in 1915 describing a submarine fitted with mine-evading devices and meant to under-run nets, which has been reproduced in the previous chapter. [Illustration: THE U-65 Photograph copyright by Underwood & Underwood One of the large German U-boats fitted with deck guns hailing a Spanish merchantman which they have held up.] [Illustration: RUSSIAN-LAKE TYPE These vessels are powerfully armed, fitted with four torpedo tubes firing fore and aft, also Dzrewiecke apparatus for firing torpedoes to either broadside.]