History of the Atlantic Cable & Undersea Communications
from the first submarine cable of 1850 to the worldwide fiber optic network

Coaxial Commonwealth Cables
by Stewart Ash

Coaxial Commonwealth Cables

On the 25 September 1956, the first telephone call across the Atlantic over a submarine cable was made between London, New York and Ottawa. TAT-1 (Trans-Atlantic Telephone 1) comprised two coaxial cables containing unidirectional valve amplifiers designed by Bell Labs. These amplifiers, generally referred to as repeaters, were housed in flexible units that could be integrated into the cable structure and pass through existing cable laying machinery. They were capable of delivering 36 x 4kHz voice circuits, each of these being the equivalent of 25 telegraph circuits. All the cable was armoured; 7,739km was made at the Submarine Cable Ltd (SCL) Enderby Wharf factory in Greenwich and its new Ocean Works factory in Erith, Kent, UK, especially built for the project. 616km of shallow water cable was manufactured at the Simplex Wire and Cable Co in New Hampshire, USA.

Due to the success of TAT-1, in May 1957 officials from the UK and Canadian Governments met in Montreal and agreed in principle to lay a transatlantic telephone cable between their two countries. This agreement was formalised in February 1958 with the announcement of the CANTAT (Canadian Trans-Atlantic Telephone) project. This cable was to incorporate the latest British engineering developments and deliver 80 x 4kHz circuits over a single cable.

In June 1958, a Commonwealth Telecommunications Conference was held in London. The main agenda item was how to extend telephonic connectivity around the Commonwealth. The conference recommended that the CANTAT concept should be extended to develop a round-the world network of large capacity cable systems. The eastern routing suggested was UK, South Africa, East Africa, Colombo (with spurs to Karachi and Bombay) on to Penang (with a spur to Chittagong) and finally to Australia. The western route would comprise CANTAT from the UK to Canada, microwave links across Canada to Vancouver, and then submarine cable to Australia and New Zealand.

In 1959, the Australian Government invited Commonwealth countries to a conference in Sydney, where it was agreed that on completion of CANTAT a new system called COMPAC (Commonwealth Pacific Cable) would be laid across the Pacific from Vancouver to Australia and New Zealand. The eastern route was dealt a severe blow when on 31 May 1961 the Union of South Africa declared itself a republic, outside the Commonwealth, and withdrew from the project. As a result, nine representatives of Commonwealth countries met in Kuala Lumpa, hosted by the Government of the Federation of Malaya, to discuss a coaxial cable to connect Australia to South East Asia, to be called SEACOM. It was agreed that the project would be jointly funded by the UK, Canada, Australia, the Federation of Malaya, Hong Kong and Singapore. In 1962, these six countries reconvened in Kuala Lumpa where they agreed their respective contributions and the final routing, which included a landing in Guam, agreement for which was to be obtained by the Australians.

With TAT-1 in mind, in 1952 the British Post Office (BPO) and Cable & Wireless Ltd had launched a joint research project, with SCL and Standard Telephones and Cables Ltd (STC), into cable and repeater design. The research team was led by the BPO’s Director of Research, Reg Halsey, at their Dollis Hill laboratories. This joint team came up with some major technical innovations.

Firstly, in parallel with Bell Labs flexible repeater development, the British developed a rigid repeater housing which could be jointed in line with the cable. Within the housing, there was room for band pass filters which allowed bi-directional transmission over a single cable. This design had been available for TAT-1 but because of the difficulty of laying the housing and bypassing the cable machinery it was not adopted. The solution was a bypass rope attached to the cable in front and behind the repeater. The bypass rope passed through the cable machinery and the repeater was carried passed on a trolley. Once this technique had been proved, it remained the method for deploying repeaters until the introduction of the Linear Cable Engine (LCE) in 1971.

Perhaps the greatest innovation was the development of Lightweight (LW) cable. Up to this point, the strength of the cable had always been provided by external armour wires. The LW coaxial cable had a high tensile steel core overlaid with a copper conductor, a dielectric of polyethylene, a copper or aluminium outer conductor, and finally a higher density polyethylene outer sheath to provide abrasion protection. The overall diameter was just less than one inch (0.990”).

It was believed that supporting the weight of the repeater, in a LW catenary, would cause excess strain on the cable or cause cable run-away. A method was needed to relieve this additional strain. The answer was to attach parachutes to the repeaters when they were deployed, the theory being that the parachute would open in the water column and bear some of the weight of the repeater during its descent to the seabed. Successful trials were completed in Loch Fyne in 1960, and parachutes were used on all British manufactured repeaters deployed in deep water until the introduction of a new, stronger, one and a half inch (1.47”) cable design in 1968, after which time the practice was abandoned.

In order to accomplish the installation and to maintain the Commonwealth Cables, a number of new cable ships, purpose-built for handling rigid repeaters and LW coaxial cables, were commissioned by Cable & Wireless:

CS Retriever 5; 4,000 tons; launched 1961

CS Mercury; 8,962 tons; launched 1962

CS Cable Enterprise; 4,085 tons; launched 1964

CS Mercury loading SEACOM at SCL Greenwich on 23 August 1965

Some facts about these three systems:

CANTAT: Oban, Scotland - Corner Brook, Newfoundland 3,864km. Cable manufactured by SCL (Greenwich and Erith) and STC (Southampton). Repeaters manufactured by SCL (Greenwich) and STC (North Woolwich). Repeater spacing 48.23km; initial system capacity 60 x 4kHz voice channels, upgraded to 80 x 3kHz voice channels. Cable ships used; CS Monarch 4 (from 1971 CS Sentinel), CS Ariel and CS Albert J Myer. The system was inaugurated by HRH Queen Elizabeth II on 19 December 1961. Project cost £9M.

COMPAC: Comprised five segments: Vancouver - Port Alberni 150.28km; Port Alberni - Keawaula Bay, Oahu 4,723.59km; Keawaula Bay - Suva, Fiji 5,701.34km; Suva - Auckland, New Zealand 2,337.68km; Auckland - Sydney, Australia 2,361.80km. Cable and repeaters manufactured by SCL and STC. Repeater spacing 48.23km; initial system capacity 80 x 3kHz voice channels, upgraded to 82 x 3kHz voice channels. Cable ships used; CS Monarch 4, CS Mercury and CS Retriever 5. The system was inaugurated by HRH Queen Elizabeth II on 2 December 1963. Project cost £28M. It was described at the time as the world’s largest telecommunication project.

SEACOM: Comprised five segments and was installed in two phases. Phase 1: Katong, Singapore - Kota Kinabalu, Malaya 1,608.55km; Kota Kinabalu - Deep Water Bay, Hong Kong 2,044.54km; Deep Water Bay - Tumon Bay, Guam 3,916.54km. Cable and repeaters manufactured by SCL and STC. Repeater spacing 48.23km; initial system capacity 80 x 3kHz voice channels, upgraded to 82 x 3kHz voice channels. Cable ships used; CS Monarch 4, CS Mercury, CS Retriever 5 and CS Recorder 3. Phase 1 was opened to the public on 31 March 1963. Phase 2: Cairns, Australia - Madang, Papua New Guinea 2,994.45km; Madang - Tumon Bay 2,580.72km. Cable and repeaters manufactured by SCL and STC. Repeater spacing 48.23km; initial system capacity 160 x 3kHz voice channels, upgraded to 166 x 3kHz voice channels. Cable ships used CS Monarch 4 and CS Mercury. The entire SECOM network was formally inaugurated by HRH Queen Elizabeth II on 31 March 1967. Project cost £24M.

CS Cable Enterprise, built to maintain the Commonwealth Cables

A capacity of 166 voice circuits is infinitesimal when compared with today’s Terabit systems; however, 50 years ago it was leading edge technology. The Commonwealth Cables revolutionized the design of deep water cable, repeater housings, and the cable ships that laid and repaired them.


Article text copyright © 2016 Stewart Ash


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Last revised: 9 October, 2016

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