30 
If the depth of detonation D is increased slightly the initial 
appearance of the plume is slightly changed because the gas pressure on 
venting is reduced. The dimensions of the cloud zone diminish with the 
respect, to the diameter of the stem until for a depth of detonation D 
where W3/D is about 1.3 1b.3 feet! the cloud zone width equals that of 
the sten at maximm growth, iee. about 20 charge diameters. The mechanian 
of stem and jet formation is, however, fundamentally unaltered. For 
geometrically similar shallow underwater explosions of different scales, 
the dimensions of the various plume features scale roughly as the linear 
dimensions of the experiment or as the cube root of the charge weight. 
Some idea of the heights attained by the jets from such shallow 
underwater explosions is afforded by the following figures. A 10 lbs. 
charge of P.E. No. 2 at a depth of 1.6 feet, i.e. where wy = 1.3 forms 
a jet which reaches a height of over 200,feet. A 300 lbs. depth charge 
fired at 5 ft. below the surface, ise. W3/D = 1.4 forms a jet which reaches 
over 600 feet and is only about 30 to 40 feet in diameter. 
. Fig.1 
CLovo zone, 
UNosRweatTsR CAVITY 
