Final inspection and as- 

 sembly of one of the 

 thirty "turtles" specially 

 designed by the BuOrd 

 Instrumentation Group 

 for recording pressure 

 produced on the lagoon 

 bottom by the huge 

 waves generated by the 

 B-Day underwater explo- 

 sion. Pressure elements 

 were of the Bourdon 

 type, being actuated by 

 water forced in by ex- 

 cessive external pressure. 

 Water entered through a 

 fine capillary serving as 

 a protective frequency 

 filter. 



Ready to plant a turtle 

 on the bottom of the la- 

 goon. The turtle cases 

 were made of very heavy 

 steel to prevent their del- 

 icate contents from being 

 flattened by the ex- 

 tremely intense under- 

 water shock wave. For 

 ease of recovery the tur- 

 tles were attached to tar- 

 get vessels or special 

 buoys by means of slack 

 steel cables. However, 

 several of the turtles 

 placed near the center of 

 the underwater explosion 

 were never seen again. 



Plate 15 



