244 



Popular Science Monthly 



>. — Line of vision 



m 



Sarlace of Ocean 



sT 



Position No6- 

 Smoke appears 200 Ft. 

 above water 



Position No 5 

 Lusitania type surface 

 5hijp;top of smoke stack 

 100 Ft. above water 



Position No. 4. 

 Merchant tramp., 

 surface ship; top" 

 of smoke stack 

 40 Ft above water 



How the Submarine Takes Advantage of Her Low-Lying Hull 



This diagram, shows the comparative visibility 

 of vessels when seen from a military submarine 

 and gives the distances at which the various parts 

 of a large ocean steamer such as the Mauretania, 

 with smoke-stacks extending one hundred feet 

 above the surface of the sea, would be visible to a 

 distant observer fifteen feet above the surface. 

 Assume that the Mauretania is making her maxi- 

 mum speed of about twenty-five knots. By re- 

 ferring to the diagram it is seen that her upper 

 works become visible above the horizon at a dis- 

 tance of eighteen and three-eighth miles from the 

 periscope of the submarine. By using his range 



She eluded not only the hundreds of 

 vessels which swarm in the waters sur- 

 rounding Great Britain and which are 

 constantly on the watch for submarines, 

 not only the seaplanes and dirigibles 

 which patrol the British coast, but also 

 the British cruisers on the Atlantic sea- 

 board of the United States. No vessel 

 spoke her on the way. She entered 



'^;;^^V^>-,.. 



and direction finder, the submarine commander 

 can determine the course of the vessel and figure 

 out just when and where he can intercept her 

 (position No. 5). In the case of a slow tramp, the 

 smoke from the stack will first betray her approach. 

 Her smokestacks are probably not over forty feet 

 above the water level; therefore, if she were making 

 the same course as the high-speed ship, it would 

 be observed by referring to position No. 4 and the 

 data there given, that the submarine at a speed of 

 ten knots has more time to get nearer the course of 

 the approaching ship and can have more time to 

 calculate the enemy's speed of approach and 



Baltimore and New London with dra- 

 matic unexpectedness, unloaded her coal- 

 tar dyes, shipped a new cargo of nickel 

 and other German necessities, and calmly 

 sailed for home. 



In my judgment the only way in which 

 we can thwart the submarine, the only 

 way in which we can continue to send 

 much-needed fuel, food and supplies to 

 our Allies is the construction of large 

 merchant submarines like the Deutsche 



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Vioqram poiifion Kos 

 Luiitania type. 

 Speed J5 knoti 



Why a Cargo- Carrying Submarine Can Cross the Atlantic Ocean 



Diagram position No ♦ 

 merchant tramp. 

 Speed 10 knots 



Diaqrann position No i 

 cargo submarine. 

 Speed II Knots 



A cargo-carrying subm irinc. traveling with a 

 freeboard of five feet wouM become visilile to a 

 submarine lying in ambusli when she approached 

 within eight miles. This iiureases tlic area from 

 one hundred and three sfinaro miles as shown in 

 position No. 1, to two huiulrcd and one square 

 miles as shown in position N'o. 2. In comparison 

 with the usual tyjre of surfaci- cirKo-iarrvinK ship — 



a tramp, for instance. — the submariiio freighter is 

 siife; for she has the ability to submerge in less 

 tiian two tuiinite.>!. Moreover, it is hardly likely 

 that sill- will be attacked without warning for fear 

 she might be a friendly military submarine. When 

 far from land, she could navigate entirely on the 

 surface with a freeboard of fifteen feet, in which 

 condition she can make a speed of eleven knots as 



