It may safely be said that no difficulty will be found in getting sailors to form the crew of a submarine boat in time of war. Great Britain, the United States, France, and other great naval Powers have only to call, and hundreds of brave fellows will volunteer, however great the odds against which they may have to fight. This being the case, our naval constructors must see to it that every precaution is taken to make the boats as safe and as habitable as possible. The accidents to which a submarine is subject are many. The most serious is passing the safe limit of depth. If she descends beneath this limit the pressure will increase; her hull will be battered in; she will diminish in volume; her downward course will be rapidly accentuated, and there must inevitably follow the crushing in of the boat and the death of the crew. [Illustration: THE ARMAMENT AND THE PERISCOPE OF THE “GOUBET.” ] For every boat there is a limiting depth, beyond which she must not go. While it is quite possible to construct a boat strong enough to resist the pressure at depths of 50 fathoms and over, it will not be necessary to go deeper than 5 to 6 fathoms, or enough to clear the keel of a big ship. Still it will be well to give the boat a hull capable of resisting pressures greater than those she will normally encounter. By means of a hydrostatic valve or some similar arrangement, the submarine may be kept from diving to too great depths. It is said that the “Goubet” boats can withstand the pressure at a depth of about 5,000 feet, or very nearly a mile beneath the surface; the “Holland” boats can navigate with safety at 150 feet, a depth quite sufficient for all practical purposes. The French submersible _Silure_ was recently sunk to a depth of 134½ feet, and it was found that the hull was compressed to the extent of 1–25th of an inch. No inconvenience was felt by the crew greater than that experienced at a depth of 20 feet. Submarines possessing floatability have the power of rising to the surface should any accident happen to the motive power, steering gear, machinery, &c., and automatic arrangements are provided for working the horizontal rudders in order to keep the boat on an even keel. Some accident might, however, cause the boat to begin to sink, and the advisability of the submarine carrying a false bottom or detachable keel has been pointed out, as this could be dropped in an emergency, causing the vessel to rise at once to the surface.