usedo Motion picture cameras could catch the behavior at water 

 impact and underwater cameras the subsequent behavior Thus 

 it was possible to get accurate information on underwater 

 trajectory and speed of descent » 



For fuze studies the fuze mechanism could be modified so 

 that a click, which would be picked up by the hydrophones, 

 would indicate the depth at which arming had taken place Fuze 

 functioning on impact could be studied by submerging a target 

 and modifying the fuze so that a click was substituted for 

 normal detonation,, In this way it was possible to tell at what 

 angles of impact and against what substances -- for instance, 

 the steel plate or wooden deck grating of a submarine -= satis- 

 factory fuze functioning could be expected,, 



In order to carry on fundamental studies, a second lab- 

 oratory was set up to study entry and underwater-trajectory 

 behavior of small-scale models „ The equipment of this lab- 

 oratory consisted of a glass-sided tank and a launching device 

 operated on the cross-bow principle „ The latter could be ad- 

 justed to give a variety of entry angles and entry speeds. 

 High-speed cameras, including a rotating disc camera, set 

 facing the glass side of the tank and synchronized with the 

 trigger of the launching mechanism, recorded the entry and 

 subsequent trajectory of the model „ 



In this way, a considerable amount of information was 

 accumulated concerning the behavior of models with a variety 

 of head or nose shapes,, As any projectile -- model or full 

 scale -- enters the water, it carries with it air which forms 

 a bubble o The shape of the entering portion of the projectile 

 determines the size and shape of the bubble. As the projectile 

 goes through the water, the bubble attenuates and finally 

 collapses, the trajectory being determined to a considerable 

 extent by the shape of the bubble and the position of the 

 projectile in relation to it » The photographs made of launch- 

 ings in the model tank gave a very detailed record of bubble 

 phenomena o 



When the torpedo-launching station (described in the 

 next section) was working with full-size aerial torpedoes, 

 accurately built scale-models, one inch in diameter, were 

 tested in the mcdel tanko Comparisons of full-scale and 

 model launchings showed that small-scale tests could not be 

 extrapolated to prototype size without danger of erroneous 

 conclusions on entry phenomena „ Modification of the models 

 resulted in behavior more consistent with the performance of 



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