250 -4- 



the change In the shape of the gas bubble. The migrating gas 

 bubble does not retain its spherical shape, but flattens out 

 in a plane perpendicular to the direction of the motion. 

 The result is a deceleration of the bubble and, as a conse- 

 quence, an intensification of the pressure pulse. Prelim- 

 inary studies of this effect have been carried out independently 

 in England and at N.Y.U. by Dr. Shlffman [8]. 



Finally, the still unsolved problems presented by the 

 striking phenomena occurring at the water surface must be 

 mentioned. A proper interpretation of the "domes" and 

 "pltunes" rising into the air above the explosion should yield 

 much information concerning the process taking place under 

 water. 



The effect of gravity in moving the bubble closer to 

 the target is not the only factor which leads to increased 

 damage by the second pulse. Another element of major im- 

 portance, emphasized by Shiffman and Friedman, is that the 

 peak pressvire of the second pulse depends greatly on the 

 state of motion of the bubble at the moment of the first 

 contraction. It Is shown that the peak pressure of the sec- 

 ond pulse possesses a decided maximum if the gas bubble is 

 stationary at the moment of contraction. For deptlis of 

 water and weights of explosives actually used, it is indeed 

 possible to keep the bubble stationary by counterbalancing 

 the gravitational force with the attractive force of the 

 sea bed and the repulsive force of the water surface. 



This principle of stabilization forms the main point 

 of the following report. It is assiimed that the mine is to 

 be placed fairly close to the sea bed, but not necessarily 

 directly on it, and it is then found (roughly stated) that 

 for mines of about 500 to 2000 lbs. of explosive in water 

 about 70 to 150 ft. deep, the optimal position is about one 



