TEST B: UNDERWATER EXPLOSION 



greater than a mile per second. Almost at once the 

 rate decreased sharply ; the growth was very slow after 

 the first five seconds. The altitude reached at the end of 

 fifteen seconds was about one mile; at the end of the 

 first minute, the altitude was about one and one-half 

 miles. 



The rising mass of water passed rapidly from the 

 ''hair-do" stage to the crowned funnel stage and finally 

 to the full cauliflower stage. Judging from photo- 

 graphs taken from drone planes flying directly above, 

 the cauliflower appeared to have a relativeh^ hollow 

 center. The diameter of the cauliflower sixty seconds 

 after Mike Hour was greater than one and one-half 

 miles. The diameter of the column or stem itself was 

 roughly 2000 ft. 



Rising in the column were various fragments, pre- 

 sumably from LSM-60 but possibly from the lagoon 

 bottom. Several of the larger fragments left in their- 

 wake white condensation trails, called bright tracks. 

 A number of the fragments struck the surface of the 

 water roughly a mile away. 



Great black blotches appeared in the side of the 

 column. One blotch was as large as a battleship. The 

 cause of these blotches is not known with certainty. 

 One theory is that they consisted of dust and soot 

 sucked up from the target vessels. The largest of the 

 big dark areas, which appeared near the location of 

 the ARKANSAS, may not have been a true blotch at 

 all ; perhaps it was a cavernous hole in the side of the 



155 



