WHY OPERATION CROSSROADS? 



had been hoped; real gaps remained. And then, of 

 course, no ships were involved. 



At Hiroshima and Nagasaki a few photographs and 

 pressure measurements were made of the explosions, 

 but almost nothing of value to physicists was learned. 

 Physicists wanted actual values of the following: 

 pressure, impulse, accelerations, shock-wave velocity, 

 ranges and intensities of gamma radiation, ranges and 

 intensities of neutron radiation, decrease of the 

 gamma radiation during the first few hours. And med- 

 ical men, arriving on the scene late, found it difficult 

 to tell w^hat the early symptoms of the injured persons 

 had been, and whether the injuries resulted primarily 

 from flash burn, gamma radiation, or from secondary 

 factors such as fires, and floods, lack of food, over-exer- 

 tion, and lack of medical attention. 



Nor could model tests give the pl\ysicists their an- 

 swers. At least four serious obstacles stood in the 

 way. First, you can't make a model atomic bomb; you 

 have to use TNT. To imitate even a small ''model" 

 atomic bomb, you use an enormous pile of TNT, and 

 the pile is so enormous that the whole test is spoiled, 

 at least as far as close-in events are concerned. 



Second, model making is not the simple matter it 

 may appear to hobby-shop artists; a model ship, for 

 example, has to be not only the same shape as the 

 actual ship, but the model's sides and decks must 

 be almost perfectly to scale also. This means that the 

 sides of a model transport ship, for example, must be 



