14 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1957 



cable. The structure ultimately evolved, consisting of two over-lapping 

 layers of abutting steel pressure rings within a flexible waterproof con- 

 tainer, was an important influence on the electrical design, since it placed 

 severe limitations on size and placement of individual components. 



Because these repeaters were to lie without failure for many years on 

 the ocean bottom, it was necessary either to provide a minimum number 

 of components of the utmost reliability, or to provide duplicate com- 

 ponents to take over in case of failure. The size limitation favored the 

 former approach. Similarly, the need for small size and minimum number 

 of components militated against the use of tw^o-way repeaters with their 

 associated directional filters. 



Out of these considerations grew the Bell System approach to solving 

 the transatlantic problem by the use of two cables, each with built-in 

 flexible amplifiers containing the minimum number of components of 

 utmost reliability and a life objective of 20 years or better. 



It was not until the end of World War II that such a system could be 

 tried. At this time it was decided to install a pair of cables on the Key 

 West-Havana route to evaluate the transatlantic design which had 

 evolved in the prewar years. After further laying trials, this plan was 

 completed in May, 1950, with the laying of two cables. Each of these 

 had three built-in repeaters lying at depths up to 950 fathoms. These 

 cables, each about 120 nautical-miles in length, carry 24 telephone 

 circuits. They have now been in continuous service for over six years 

 without repeater failure or evidence of deterioration. 



EARLY TRANSATLANTIC TECHNICAL DECISIONS 



Early in 1952, negotiations concerning a transatlantic cable were 

 again opened between the American Telephone and Telegraph Companj^ 

 and the British Post Office. As indicated above, at that time each party 

 had been laying plans for such a system. Thus it became necessary to 

 evaluate the work on each side of the Atlantic to evolve the best techni- 

 cal solution. 



To do this, a technical team from the Post Office visited Bell Telephone 

 Laboratories in the fall of 1952 to examine developments in the United 

 States. The w^ork of the preceding 30 years was reviewed in detail with 

 particular emphasis on the development and manufacture of the 1950 

 Key West-Havana cables. This was followed by a visit to the Post 

 Office by a Bell Laboratories' team to review similar work in Great Brit- 

 ain. Again the review was comprehensive, covering shallow-water sys- 

 tems as well as plans for deep-water repeaters. Each visit was charac- 

 terized by a frankness and complete openness of discussion that is 

 perhaps luiusual in international negotiations. 



