City of Light: The Story of Fiber Optics

SUBMARINE CABLES 203
for its success was the use of gutta percha, a hard plastic made from the sap
of tropical trees that remained the standard insulator until the invention of
polyethylene in the late 1930s. Another was that telegraph signals did not
need amplification. Telephone signals did, so long-distance calling on land
had to await the invention of the vacuum tube. Early tubes were not ready
to go to the bottom of the sea; they drew too much power and could not
withstand the pressure. Instead, transatlantic telephony began with wireless
transmitters.
World War II highlighted the limits of radio telephones. Transmission was
noisy, vulnerable to changes in the atmosphere, insecure, and limited to 15
or 16 channels. 4 The war also brought new durable, compact, and low-power
vacuum tubes, which the British Post Office put into the first submerged
repeater in the Irish Sea in 1943. AT&T used them in a 1950 cable between
Key West and Havana that remained America’s only direct link to Cuba until
1989. 5
Satisfied that the shorter systems worked, the Post Office and AT&T agreed
in 1953 to lay TAT-1, the first transatlantic telephone cable. The cautious
phone companies didn’t trust new-fangled transistors, so they equipped the
pair of coaxial cables that ran 1,950 miles (3,100 kilometers) from Newfoundland
to Scotland with 51 vacuum-tube repeaters each. On September 25,
1956—a little over a year before Sputnik—the system started carrying 36
telephone circuits, one cable carrying the eastbound voices, the other the
westbound signals. It cost about a million dollars per two-way channel and
was used until 1979. 6
More cables followed, with fatter coaxial cables that carried more channels.
Massive, costly cables crossed the Pacific, stopping at Hawaii on their way to
Japan and Australia, tying the world together. Manufacturers replaced heavy
steel armor with a thick plastic covering for deep sea areas where cable damage
was unlikely, but were slow to adapt other new technology. They did not
lay the first transistorized repeater until 1968. 7
Submarine coax technology reached its high point in the sixth cable from
the United States to Europe, TAT-6, which in 1976 added 4000 new voice
circuits to the 1200 of the five previous TATs. At $179 million, TAT-6 cost
more than double TAT-5, but the cost per circuit was $45,000—less than
half that of TAT-5. The TAT consortium immediately started work on a duplicate,
called TAT-7, to add 4000 more circuits in 1983. 8
The End of the Line for Coaxial Cable
Engineers had developed many tricks to squeeze the most out of submarine
cables, such as packing five conversations into a single transatlantic voice
circuit. However, TAT-6 and-7 were at the practical limits of coax technology.
Increasing the number of voice circuits required transmitting at higher
frequencies, but higher frequencies suffer more loss in coaxial cables. Offsetting
the higher loss required adding more repeaters and reducing the distance