Once upon a time in the no so distant past, thousands of Bell System employees worked in underground facilities to insure whenever the "Balloon Went UP", the President and all the key government and defense officials would have instant access to each other as well as our nuclear forces and civilian defense agencies.  Many of these key circuits had constant monitoring devices and should a circuit (many of which were thousands of miles long and ran through dozens of switching centers) fail, the technicians had 3 minutes repair or reroute the circuits).  These were the days before fiber and reliable, hardened satellites.  thus the backbone of this system was the L Carrier Coaxial System. It was referred to as the L CXR system or publicly as the  Transcontinental Cable.

The L Carrier system was developed prior to World War II as a high capacity telephone as well as television transmission system.  The cable and repeaters were buried underground to take advantage of the constant temperature (approximately 50 degrees).  Prior to the war planning had begun to triple the bandwidth of the L-1 system to 7 mhz and be able to put 1800 circuits on a single coaxial cable.  This system would be the L-3 system.  After the war L-3 routes began to link major metropolitan areas together across the country.  Some L-1 and L-3 cable were installed for strictly military purposes at facilities like Cheyenne Mountain, but mainly L-1 and L-3 were used for civilian traffic.  As the Cold War went into full swing, L-3 was chosen as the primary transmission medium for defense critical circuits.  Main stations linking coaxial cable routes together were fully hardened to withstand a 20 megaton blast 2 1/2 miles away.

In general main stations were locating at least 20 miles away from major cities to lessen the chance of a direct hit.  After the Cuban Missile Crisis the newly former National Communications System, codeveloped the AUTOVON stand alone defense telephone system and co located the AUTOVON switching centers in the main stations.  Main stations were also equipped with nuclear blast detectors that in addition to closing the main station's blast valves, relayed the blast signal to an underground civil defense center outside Washington, DC to indicate areas that had received nuclear blasts.  Some main stations were even designated reception centers for key governmental during Armageddon.

In the 70's and 80's routes were upgraded from tubes to transistors.  Coaxial cables were increased from 8 to 12 to 20 and finally 22 tubes per cable.  Repeater were made more reliable and cable and repeater troubles could be automatically located from the equipment in the main station.  To increase bandwidth repeater spacing was reduced from 8 mile to 4 miles to 2 miles  and finally 1 mile.  Eventually a single L-5 cable could carry 108,000 circuits.

With the end of the Cold War coming the Coaxial System faced additional difficulties.  The breakup of the Bell System gave AT&T the Coaxial Routes, and no longer could the defense related cost be passed on to the consumer.  MCI and other companies began laying fiber across the United States, and the fiber did not require the main stations and associated high maintenance that the Coaxial Systems did.  AT&T lost the AUTOVON system to MCI and a successor system that was fiber optics based.  By 1990 almost all of the Coaxial Systems had been shut down.  Some of the Main Stations have an after life as fiber switching centers, and those that were lucky enough to have a tower have survived as cellular and/or other personal communications broadcast facilities.  Many have been sold off to enterprising business men to be used as record storage facilities or factories.  Some have been abandoned in place.

This web site is devoted to the L Coaxial System and associated Cold War Communications sites and systems.