A submarine communications cable is a cable laid on the sea bed between land-based stations to carry telecommunication signals across stretches of ocean. The first submarine communications cables, laid in the 1850s, carried telegraphy traffic. Subsequent generations of cables carried telephone traffic, then data communications traffic. Modern cables use optical fiber technology to carry digital data, which includes telephone, Internet and private data traffic.

Modern cables are typically about 1 inch (25 mm) in diameter and weigh around 2.5 tons per mile (1.4 tonnes per km) for the deep-sea sections which comprise the majority of the run, although larger and heavier cables are used for shallow-water sections near shore. Submarine cables connected all the world’s continents except Antarctica when Java was connected to Darwin, Northern Territory, Australia in 1871 in anticipation of the completion of the Australian Overland Telegraph Line in 1872 connecting to Adelaide, South Australia and thence to the rest of Australia.

Importance of submarine cables

As of 2006, overseas satellite links accounted for only 1 percent of international traffic, while the remainder was carried by undersea cable. The reliability of submarine cables is high, especially when (as noted above) multiple paths are available in the event of a cable break. Also, the total carrying capacity of submarine cables is in the terabits per second, while satellites typically offer only 1000 megabits per second and display higher latency. However, a typical multi-terabit, transoceanic submarine cable system costs several hundred million dollars to construct.

As a result of these cables’ cost and usefulness, they are highly valued not only by the corporations building and operating them for profit, but also by national governments. For instance, the Australian government considers its submarine cable systems to be “vital to the national economy”. Accordingly, the Australian Communications and Media Authority (ACMA) has created protection zones that restrict activities that could potentially damage cables linking Australia to the rest of the world. The ACMA also regulates all projects to install new submarine cables.

Notable events

The Newfoundland earthquake of 1929 broke a series of trans-Atlantic cables by triggering a massive undersea mudslide. The sequence of breaks helped scientists chart the progress of the mudslide.

On 26 December 2006, the 2006 Hengchun earthquake rendered numerous cables between Taiwan and Philippines inoperable.

In March 2007, pirates stole an 11-kilometre (7 mi) section of the T-V-H submarine cable that connected Thailand, Vietnam, and Hong Kong, afflicting Vietnam’s Internet users with far slower speeds. The thieves attempted to sell the 100 tons of cable as scrap.

The 2008 submarine cable disruption was a series of cable outages, two of the three Suez Canal cables, two disruptions in the Persian Gulf, and one in Malaysia. It caused massive communications disruptions to India and the Middle East.

In April 2010, the undersea cable SEA-ME-WE 4 was under an outage. The South East Asia – Middle East – Western Europe 4 (SEA-ME-WE 4) submarine communications cable system, which connects South East Asia and Europe, was reportedly cut in three places, off Palermo, Italy.

The 2011 Tōhoku earthquake and tsunami damaged a number of undersea cables that make landings in Japan, including:

  • APCN-2, an intra-Asian cable that forms a ring linking China, Hong Kong, Japan, the Republic of Korea, Malaysia, the Philippines, Singapore, and Taiwan
  • Pacific Crossing West and Pacific Crossing North
  • Segments of the East Asia Crossing network (reported by PacNet)
  • A segment of the Japan–U.S. Cable Network (reported by Korea Telecom)
  • PC-1 submarine cable system (reported by NTT)

In February 2012, breaks in the EASSy and TEAMS cables disconnected about half of the networks in Kenya and Uganda from the global Internet.

In March 2013, the SEA-ME-WE-4 connection from France to Singapore was cut by divers near Egypt.

In November 2014 the SEA-ME-WE 3 stopped all traffic from Perth, Australia to Singapore due to an unknown cable fault.