Although the thermistor chain is admirably suited to survey 

 purposes in the upper 300 meters of the ocean, the time taken for reeling 

 out and in, and the fact that the ship's velocity must be low to ensure 

 that the chain is quasi-vertical, preclude the use of such devices in 

 tactical situations. There seems to be little reason why, considering 

 current ability in towing technology, a similar system could not be adapted 

 to considerably greater depths and be used to survey the semi-permanent 

 deep sound channels, but it might not be competitive with a system using 

 fixed vertical stations and research submersibles investigating the hetero- 

 geneity between the stations. It also seems possible that the use of 

 suitable powered depressors on the fish could make it possible to hold the 

 chain stable at steep angles at higher ship velocities. 



C. Reversing Thermometers and Bathythermographs 



Reversing thermometers and mechanical bathythermographs are 

 the usual methods of obtaining temperature profiles in the ocean and 

 our present records of subsurface temperature structure consist almost 

 entirely of data by these two instruments. Both systems are well estab- 

 lished and are described in many references (e.g., Reference 21). Table 

 II-l, taken from that reference, compares the two systems and also the 

 author's suggestion of an "ideal" general purpose instrument. In fact the 

 numbers quoted there for the mechanical bathythermography are generally 

 too optimistic. 



D. Expendable Bathythermograph 



The need for apparatus improved for tactical situations from 



20 



Arthur ZB.lUttlcJnr. 



