SCIENTIFIC OFFENSIVE 



a wave avoids suddenness: like an ocean swell, the 

 pressure increases gradually and then decreases grad- 

 ually. 



But a shock wave has a personality of its own. In 

 the first place, its intensity is so great that it cannot 

 be content with spreading at the usual velocity — the 

 velocity of the fastest jet planes; it demands higher 

 velocity, equal to that of the fastest bullets. The more 

 intense the shock wave, the higher its velocity. Sec- 

 ondly, the pressure does not arrive at any given point 

 gradually, but all at once. A building, tree, or ship may 

 be enjoying an uneventful existence at one instant, but 

 an instant later it may be reeling under the full im- 

 pact by the pressure wave. There is absolutely no 

 warning. The destructive effect is diabolically maxi- 

 mized.* 



The most energetic explosions produce the most in- 

 tense pressures and the most unusual Shockwaves. The 

 experts at Bikini therefore went to great lengths to 

 measure the A-Day shockwave. Spearheading the at- 

 tempts to measure shockwave velocity was a group of 

 high-speed cameras. Some of these, located atop special 

 towers on Amen Island, were operated automatically 

 and were capable of taking over 500 individual pictures 

 each second. By use of short exposure times, and, of 

 course, long focal length lenses. Captain R. S. Quacken- 



* This suddenness, or vertical front phenomenon, is due to tlie 

 tendency of the hack part of the pressure wave to catch up with — 

 and, so to speak, ride on the shoidders of — the front part. The 

 result is of sledge-hammer severity. 



73 



