Page:Popular Science Monthly Volume 92.djvu/262

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��Popular Science Monthly

��found in the use of the smoke screens ad- vocated by the Government. Smoke is exactly what the German submarine com- mander is looking for. The sea captain obliges him by throwing overboard a fuming box made according to Govern- ment specifications. The submarine sub- merges in advance of the smoke, rises within the smoke pall, gages the distance of the surface vessel with her several detectors and then plants one or more torpedoes successfully. Over fifty per cent of the vessels attacked are sunk. The smoke even hides the wake of the torpedo itself ; it removes the only chance to escape which the vessel might have.

I have illustrated this article with a few diagrams showing, the advantage of various types of vessels in evading the submarine. The captions beneath the diagrams will explain the points illus- trated. Here, it may be stated as a general principle, that visibility and speed depend upon elevation above water-level. When the sun or moon sinks beneath the horizon they cannot be seen. Neither can anything else be seen which is below the horizon. Such is the curvature of the earth that a hill of water intervenes.

It is obvious that absolute safety could be attained if a submarine cargo-carrier could travel entirely under water. That is at present impossible for good technical reasons. But a cargo-carrying submarine running awash, with her periscope and air-intakes just above the waterline may approach within about five and three- quarter miles of any waiting military sub- marine without danger of being seen. Her wake would be below the horizon. Such cargo-carrying submarines can be built and can cross the Atlantic Ocean in this condition, at a speed of about ten knots. If a sharp lookout is maintained, they have as much chance of seeing a German submarine as the German sub-

��marine has of seeing them. By the ap- plication of certain tried devices, which I do not feel it proper to divulge at this time, but which are within the knowledge of our Government authorities, in my opinion, the range of visibility can be re- duced to less than one mile. The cargo- carrier can become entirely invisible by submerging. If she travels with a free- board of five feet, she will become visible to a German submarine when she ap- proaches within eight miles." In two minutes, she can dive under water. It is hardly likely that she will be attacked without warning lest she be a friendly submarine. She will be warned by wire- less, sound, or other signals used by Ger- man submarines to communicate with one another. Her one business is to deliver her cargo and not to communicate with or expose herself to either friend or foe. When far from land, she can follow the Deutschland' s example by navigating entirely on the surface with a freeboard of fifteen feet. In that condition, she can make a speed of eleven knots without the slightest difficulty.

Sooner or later it will be recognized that the Germans are carrying on their submarine campaign, not in a haphazard fashion, but systematically. Every ship sighted by a submarine is a marked craft. Even if she is the fastest vessel afloat, she may speed unwittingly into a trap set for her by wireless. If she cannot disappear, she has no real ability to escape. On the other hand, the cargo-carrying submarine of low speed has both these advantages. She has low visibility and she can sub- merge quickly By the simple expedient of descending beneath the waves, she be- comes invulnerable She has the most valuable attribute possessed by her enemy, that of becoming invisible. You cannot successfully attack a ship whose location is unknown.

���A Lake tSubniariin. Caii^o L-ai"nt;r

��It carries 7500 tons dcail wfitilit of carKO and ran safely In- naviKated to depths of three liundred feet. Ky elitninatinK the top h;iiii|H-r and deck house used on ordinary' surface vessels, the liuU weights of such a Hubtnarinc are only sli>;lilly in excess of the hull weiglits of a box-shaped, surface, cargo-carrying ship.

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