WITH OR WITHOUT BATTLESHIPS. 89 



3,000 auxiliary patrol vessels, such as trawlers and yachts; about 100 allied submarines; 400 

 subchasers ; about 30 "mystery ships" or decoy ships, these being armed merchantmen manned 

 by naval crews and so disguised that they could not be distinguished from the unarmed 

 merchantmen ; numbers of mine layers ; also many mine sweepers used to destroy the numer- 

 ous mines which were constantly being laid by German submarines. To the above Hst of 

 vessels might be added other large naval vessels which escorted convoys across the ocean 

 until these convoys were met by the destroyers which accompanied them during the last part 

 of their voyage, except for the fact that these large naval vessels should be considered rather 

 as serving to protect against possible attacks of German surface raiders than as vessels 

 which could protect against German submarines. 



Some of the work of going to sea and escorting ships to port was carried out by airships 

 and seaplanes, operating eitlier alone or with destroyers. Aircraft must be included in the 

 forces which combined to defeat the German submarine campaign. Aircraft were exten- 

 sively used in patrolling to locate or spot submarines which were perhaps subsequently de- 

 stroyed through information obtained by the aircraft; aircraft also successfully bombed sub- 

 marines, made bombing raids on submarine bases, etc. 



Of all of the vessels and means used against German submarines the destroyers using 

 depth bombs and gunfire accomplished the greatest number of sinkings. The allied submarines 

 operating against German submarines sank more of the latter, in proportion to their number so 

 engaged, than did any other anti-submarine craft. The depth bomb was one of the most im- 

 portant factors in fighting submarines, from actual sinkings and from the demoralizing effect 

 of the explosion of such bombs in the vicinity of submarines which were not destroyed by 

 them. The use made of allied submarines and "mystery ships" in this anti-submarine war- 

 fare had a demoralizing effect which was probably more important than the number of sink- 

 ings made by these two types of vessels. Local mine fields and various forms of nets, eitlier 

 moored or towed, accomplished some of the sinkings; also, the very extensive North Sea 

 mine barrage between the coast of Norway and the Orkney Islands resulted in some sink- 

 ings of submarines, but its demoralizing effect was perhaps of greater importance than these 

 sinkings. This mine barrage, with a length of about 250 miles and a width of from 15 to 

 35 miles, contained about 70,000 mines when work on it was stopped by the armistice. 

 Had the war continued, this barrage would probably have contained several times as many 

 mines. Its construction was made possible by the invention of a mine which could be placed 

 at different depths and was exploded by a vessel striking a copper cable supported above the 

 mine by a buoy near the surface. One of these mines did the work of four mines of the 

 old t3^e which were exploded only by contact. 



Among the important devices used to detect the presence of submarines and to locate 

 them were the radio-direction finder, used to determine the direction from which wireless 

 messages sent by submarines were coming, and the improved microphones, or under-water 

 listening devices, which made it possible to detect the presence of submarines and to follow 

 their movements by sound. The microphones were made good use of by the small sub- 

 chasers operating principally in restricted waters. These vessels were armed with 3- 

 inch guns and depth bombs. They did excellent work within the limits imposed on them 

 by their comparatively small dimensions. Their work did much to keep submarines awa}' 

 from the waters patrolled by them and to prevent the submarines from making sinkings 

 and from laying mines. 



Lastly, but of great importance in this anti-submarine warfare, I must add the use 



