receiver with drastically reduced size and weight suitable for 

 aircraft use, A„ L. Thuras, starting from scratch, came up 

 with a magnetostriction hydrophone, the response characteristics 

 and the ruggedness of which were ideally suited to meet the 

 sonobuoy requirements. Meanwhile, R. I« Mason was working on 

 the difficult launching problem „ 



Beginning with the Mark II Model, various schemes were 

 tried for getting the buoy safely into the water „ After var- 

 ious attempts a Mark III unit was eventually fitted with a 

 small parachute and dropped 500 feet„ The parachute solved 

 the problem„ The buoy worked perfectly with no carrier 

 frequency shifts or other damage of any sort 



With the completion of the Mark IV- B unit, Navy and Army 

 experts were agreed that the buoy was ready for operational 

 tests . Pre-production quantities were ordered and a month 

 later, only five months after the start of the development 

 work, some of the units had already been used in actual off- 

 shore operations against the enemy,, 



The Mark IV- C and Mark IV- D buoys incorporated additional 

 improvements and final redesign was accomplished in order to 

 incorporate revisions making the unit easier to produce in 

 quantity Production models were known as AN/CRT-1 and AN/CTRT-IA. 



The sonobuoys gave the pilots of antisubmarine patrol olanes 

 what they needed - the ability to hear a submarine under water. 

 In service, they used the buoys singly in order to check sus- 

 picious signs such as oil slicks, disappearing radar blips or 

 MAD indicationSo For tracking , a number of buoys were dropped 

 in a definite pattern and the path of the submarine was traced 

 by means of the changes in the relative intensity of the sound 

 from the different locations. 



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