For defense of coast lines aeroplanes and submarines may work in conjunction. Aeroplanes, with their enormous range and high speed can locate surface ships many miles away, beyond the range of a submarine's periscope or sound-detecting devices. It could then direct the submarine by wireless or direct communication. Aeroplanes, however, are of great danger to enemy submarines. Flying at certain altitudes they can see submarines a short distance below the water and swoop down on them, dropping depth bombs or trailing torpedoes.] =Aeroplanes and Dirigibles.=--These are undoubtedly valuable near land in shallow water, _providing_ the water is clear and has a bottom in striking contrast to the hull of the submarine. I should consider the dirigible likely to prove of more value than the aeroplane, owing to its ability to hover directly over and regulate its speed to that of the submarine and thus enable itself to drop depth bombs more accurately. Experience has shown that it is almost impossible to calculate where a bomb will strike when dropped from a swiftly moving aeroplane. The chance of its striking the submarine would be very slight. The use of aeroplanes has, however, forced the submarines away from shoal clear water and probably has been instrumental, also, in causing them to become equipped with high-angle rapid-firing guns. In a battle between swiftly moving aeroplanes and submarines with high-powered guns firing shrapnel, the chances are nearly all in favor of the submarine, as they can carry the most powerful guns and are firing from a much more stable platform; in fact, the best analogy I can think of is that of a gunner in a "blind" firing at a flock of ducks passing overhead. Aeroplanes have been used, however, as scouts, merely to detect a submarine and direct surface ships to the attack; also, aeroplanes have directed trawlers to a submarine lying submerged at a shallow depth. This method of attack has undoubtedly been successful in some instances, but where success might have been met with in this manner with the earlier submarine boats, which were not provided with guns, it is now a problem easily met by submarine architects. Submarine boats may be built which have no fear of this combination. One of my earliest designs provided for a revolving armored turret to carry heavy-calibre guns; this revolvable armored turret would extend only above the surface and would carry guns of sufficient calibre to sink any trawler, destroyer, or other craft except an armored ship. It has recently been reported that the Germans are bringing out ships fitted with turrets of this type, and as they are familiar with my designs from the Patent Office specifications, and also have my working drawings of a large cruiser submarine mounted with guns, in 1905, I have no doubt that the report is true, as they have consistently been the first to adopt such new devices as may be needed to offset any attack against their submarines, or to increase