246 



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 sucli 

 a Hubtnarinc are only sli>;lilly in excess of the hull weiglits of a box-shaped, surface, cargo-carrying ship. 



