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An experimental digital repeatered line has been developed which transmits information at a rate of 224 Mb/8 as part of an experimental highspeed digital transmission system. The PCM terminals and time division multiplex portions were described by J. S. Mayo and others in the November 1965 issue of the Bell System Technical Journal. The repeatered line is described in this paper. The performance of this line is shown to be suitable for coast‐to‐coast operation. The line utilizes 0.270‐inch copper coaxial transmission lines and regenerative repeaters at one‐mile intervals. Ten repeaters have been operated in tandem to form ten miles of repeatered line. Each repeater uses 25 transistors, most of them a new germanium design with a cutoff frequency, ft, of 4 GHz. Esaki diodes provide the decision thresholds for the regeneration. Power to the repeaters is supplied by dc over the center coaxial conductor. The pulse transmission code is paired selected ternary (PST).

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This introductory paper has two objectives. The first is to offer a high‐level overview of AT&T's undersea cable technology, applications, products, and services, including installation and maintenance. This includes a relative historical cost analysis (dollars per Gbits/s per mile), as well as other high‐level growth and deployment projections to the year 2000. The second objective is to provide an overview of the articles in this theme issue on undersea communications. Here, the reader will gain an understanding of the topics and their importance to undersea communications, as well as their placement within this issue.

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