In deep water the submarine may readily escape detection by aeroplanes by sinking below the depth to which vision can penetrate. This depends upon the amount of foreign substance held in suspension in the water. Along the Atlantic coast it is possible to see only a few feet; as you go off shore vision becomes clearer, and it would probably vary during the dry seasons from four to five feet near shore to forty or fifty feet well off shore. The greatest distance I was ever able to see in my experiments in the Chesapeake Bay with a powerful searchlight was forty feet. In Long Island Sound one can seldom see over fifteen feet, and after storms, when sediment is carried into the Sound, sometimes it is difficult to see over three or four feet. I have been down on muddy bottom at a depth of one hundred feet and could not see my hand held close to my face. At a depth of one hundred and twenty-five feet in the Baltic on sandy bottom I was able to see twenty-five feet. This was about eight miles off shore, opposite Libau, Russia. In the English Channel the frequent storms stir up so much sediment that it is seldom possible to see over fifteen feet, while in the Mediterranean and our Southern waters near the Florida coast, near Nassau, and in the Caribbean Sea, it is possible at times to see seventy-five or even one hundred feet. Now there are means available to the submarine to enable it to lie at rest submerged at depths exceeding one hundred feet, and yet have a full view of surface ships and also to scan the heavens, therefore I would say that aeroplanes and dirigibles will prove ineffective against submarines fitted with revolvable turrets, high-angle firing guns, or where they may be operating in clear water exceeding one hundred feet in depth or in shallow water where the sediment held in suspension is in sufficient quantity to prevent discovery. Aviators with whom I have discussed this problem tell me they can seldom detect objects lying on the bottom, even in comparatively shallow water.
[Illustration: RUSSIAN CRUISER-LAKE TYPE SUBMARINE IN SHED BUILT BY PETER THE GREAT--1905
This was the first large submarine of the cruiser type, built substantially after the design submitted by the author to the U. S. Navy in 1901.]