Besides having proved of great value in the land campaigns, the aircraft has shown itself to be one of the most effective devices of warfare for use against the submarine, and all manner of naval craft. From the heavens they can see the submarine under the water, and as either the dirigible or the aeroplane can develop a speed greater than that of any battleship or cruiser, it is not difficult for it to soar over the vessel and drop bombs upon it. Even gas bombs have been used in the raids by the aircraft. ACCURACY THE GREAT DIFFICULTY. The difficulty in the use of bombs has been in accurately directing the death-dealing devices when the airship or aeroplane is in motion. To assist in this work aerial range finders have been devised. These are constructed on the principle of the finder on a camera, with graded scale markings to indicate the allowance that must be made for speed and motion. Complete apparatus has been built up for launching the projectiles from the large dirigibles, and to insure the missiles traveling properly vanes have been attached to some of them. In a test made under the auspices of the French Government and the Aerial Club of France, a few years ago, one of the bomb-launching machines on an aeroplane scored eleven bull's-eye shots in a target ten yards in diameter, from an altitude of more than 2000 feet, while the aeroplane was going at a speed of more than 65 miles an hour. Though there has not been any widespread use of the plan the air has been "mined" in an experimental way to protect certain sections against night raids by the airmen. Mining the air consists of locating small balloons over an area, each balloon being attached to the other with wires. The small balloons have attached to them explosive bombs which would destroy the larger aircraft if it was to run into this nest of air vessels in the dark. Reverting to the use of aircraft in naval warfare it may be said that to the aeroplane the relatively fast fleet is virtually stationary. About the only case parallel to the aeroplane looking over the hill and down on concealed enemy positions would be in rising above the smoke screen thrown out by destroyers. THE SMOKE SCREEN. The smoke screen, by the way, which has been used by the British with marked success in many instances, is an American invention. The low, swift craft are equipped with special oil burners which throw off dense volumes of heavy smoke, which float low over the surface of the water, concealing the maneuvers of the larger boats and protecting them from the skill of enemy gunners. Its effectiveness, of course, is influenced by the direction and strength of the wind. Used generously by small craft convoying a ship through a submarine area, it should be of great value. A battleship can see about as far as it can shoot, anyhow. Except for smoke screen, or the famous "low visibility," which means foggy weather or darkness, no enemy within range can be concealed.