This view shows the diving compartment being used for the purpose of grappling for the electric cables controlling fields of submarine mines. Operating in this manner, the diving compartment becomes a veritable travelling diving-bell, and when the air pressure in the diving chamber is made to balance with the water pressure outside the diving door may be opened and yet the water will not enter the working chamber.] =Dangers.=--Years of painstaking development work have eliminated most of the dangers connected with the operation of submarines in times of peace. The experienced designers have learned the importance of having great submerged stability, so that no modern craft is likely to make an unexpected headfirst dive into the mud, hard sand, or rocks on the bottom. This was a common occurrence not many years ago. Another danger to be avoided is that of asphyxiation by the escape of noxious gases from the engines. The blowing up of the vessel by the ignition of hydrogen fumes from the battery is another risk to be guarded against. In the latest vessels the noxious gases from the engine are not permitted to escape into the engine-room; gasolene is rapidly giving place to heavy-oil engines which do not use an explosive fuel, and the hydrogen gas given off during the charging of batteries is pumped overboard as rapidly as it is generated. Consequently modern submarines, when navigating on the surface, are as safe as any surface ship. In fact, they are safer, from the fact that they are so much more strongly built and that they are divided into compartments. Any one of these compartments could be filled by water in an accident and the remaining compartments would keep the ship afloat. In submerged peace-time navigation the dangers are those of collisions with surface vessels, uncharted rocks, or sunken ships. The danger of collisions with surface ships may be avoided by keeping below the depth of keel of the deepest draft surface ship, when long under-water runs are being made, and always stopping machinery to listen for the sound of surface ships before rising to the surface. If running near the surface where periscopic vision is possible, constant vigilance must be maintained, as there are no rules of the road or right of way which may be claimed by the submarine commander, owing to the fact that the lookout on the surface craft, in all probability, cannot see his little periscope in time to avoid collision. [Illustration: A MODERN SUBMARINE CRUISER, OR FLEET SUBMARINE (LAKE TYPE)