136 The Forest Products Laboratory 



out with their ship decks loaded with depth charges up to 100 in num- 

 ber and toured over the sea, dropping in a definitely ordered spiral as 

 many as 60 depth charges in 10 seconds of one another; and, of course, 

 if they did not destroy the submarine they shook up the personnel so 

 enormously that it became very unpleasant in the submarine. 



The great problem was to find where it was, and that was the 

 problem which the National Research Council wished to solve. What 

 detective device could be used to determine the position of the subma- 

 rine when completely submerged? I will not and can not give you in 

 a short time the number of devices which were attempted to detect 

 submarines. Probably if you took a large text book on physics and 

 read every chapter you would not find any physical phenomenon which 

 was not attempted, which was not utilized in some way, to attempt to 

 detect submarines by virtue of that phenomenon — light, sound, heat, 

 electricity, magnetism, everything — but the thing that seemed most 

 promising was sound, for a machine can not move without making a 

 considerable noise. Unfortunately a submarine does not make much 

 noise. The efforts we made in Wisconsin towards detecting subma- 

 rines were based upon the method of determining their position by the 

 sound they make. That is not an easy problem. 



The submarine makes a noise hke that of a humming bird in a 

 boiler factory, the factory corresponding to the ship and the humming 

 bird to the submarine to be detected. You can imagine what it would 

 be if you were clattering down a cobblestone street with a threshing 

 machine and an electric automobile was somewhere distant and you 

 were trying to determine just where the automobile was at every 

 instant. You could not do it. 



The plan which occurred to me in relation to the detecting device 

 was to work with sound in some such manner as we are familiar with 

 in light. You cannot see a star in the daytime but if you sufficiently 

 screen off the disturbing light from the skies and utilize a deep well 

 or a telescope you can see it in the daytime. If you can get some 

 method of intensifying sound from one direction only and shutting it 

 off from all other directions you might be able to detect a fair portion 

 of one sound by thus eliminating the others, and the instruments we 

 developed were based on that theory. We started working here witli 

 the generous and cordial support of the University of Wisconsin re- 

 gents. We soon moved to New London, and there under the naval 



