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

1961 CANTAT Cable

1961 Canada TransAtlantic Telephone Cable (CANTAT)

The first link in the Commonwealth Round the World Cable, CANTAT was jointly owned by Cable & Wireless and the Canadian Overseas Telecommunication Corporation (COTC). The cable was laid in two sections, known as A and B. It was the first commercial application of the new lightweight deep-sea cable.

CANTAT A: Oban, Scotland - Hampden (White Bay), Newfoundland, was manufactured by Submarine Cables Ltd.; SCL also made 90 repeater housings. Standard Telephones & Cables Ltd. made the repeater internal units. The 2072 nm ocean section was laid by HMTS Monarch (4). CS Ariel laid the UK shore ends and CS Albert J. Myer the Hampden shore ends. A 70nm link was laid overland to Corner Brook and had four repeaters laid in water or on wet ground to keep them cool. This section provided 60 4KHz telephone circuits.

CANTAT B: Corner Brook, Newfoundland - Grosses Roches, Quebec, was manufactured by Submarine Cables Ltd. together with 20 repeaters. This 400nm section was laid across the Gulf of St Lawrence by HMTS Alert (4), with CS Hadsund laying the shore ends. This section provided 120 circuits.

CANTAT was withdrawn from service in 1986. It is now generally referred to as CANTAT-1 to distinguish it from CANTAT-2, which was laid in 1974.

Site visitor William “Wally” Wyatt worked at SCL between 1955 and 1971, initially as a member of the repeater design team and later as a  divisional manager. He has very kindly provided these photos of HMTS Alert loading cable for CANTAT B at Greenwich, and the repeaters stowed and prepared for installation.

H.M.T.S. Alert loading the St. Lawrence Cable at Greenwich, June 1961

Repeaters stowed on Alert. They were powered during the crossing and were fitted with jackets carrying refrigerated water to prevent overheating.

The cable image and text below are taken from the manufacturer’s brochure.

In 1951 the Post Office proposed a radically new type of deep-sea telephone cable which is unarmoured and carries the strength member (which is essential to withstand the laying and recovery tensions) in the form of a high-tensile torsionally-balanced steel strand situated at the centre of the cable and within the inner copper conductor.

A major disadvantage which has always existed with armoured cables results from the freedom with which the cable, twisting under tension, throws turns or loops into the cable at a low tension point, which in practice is usually the sea bed. Under subsequent tension these turns develop into kinks which may seriously damage or break the cable. In this new cable deliberate attempts to produce such turns have failed, which is only to be expected since where an armoured cable would twist about 1 turn per fathom this cable would only twist by 0.001 turn.

Cable image courtesy of SCL

Composite High Tensile Steel Stress Member

        Central Copper Conductor

                Polythene Insulation

                        Aluminium Return Conductor Tapes

                                Polythene Film Separator

                                        Aluminium Screening Tapes
                                          with Polythene Film Interleaved

                                                Impregnated Protective
                                                    Cotton Tape

                                                        Polythene Sheath

The inner conductor of this new type of unarmoured cable consists of a thin longitudinal copper tape, box-seamed tightly on to the steel strand. Polythene insulation is then extruded on to the conductor and a coaxial return conductor of aluminium tapes applied, forming what is known as the "core" of a lightweight cable. It has been found necessary to include a thin aluminium tape screen to improve the crosstalk attenuation between cable flakes in the ship's tank. The cable is completed overall with a sheath of polythene. This outer protection is considered to be adequate in depths greater than about 500 fathoms where the water is generally quiet and no interference from fishing trawls or anchors is encountered.

This cable has become known as the lightweight cable because its weight in water is only one-fifth of that of a comparable armoured cable. It is also cheaper than conventional cable having a similar electrical performance and its modulus is much greater, i.e. the cable strength can support about 13 n.m. of cable in water. The size of lightweight cable adopted for CANTAT has a core diameter of 0.99" and the same overall diameter as the cable used on the first transatlantic telephone cables. Since, however, its attenuation is only two-thirds, fewer repeaters are required.

[Note: The core, noted above as having a diameter of 0.99", consists of the Steel Stress Member, the Central Copper Conductor, and the Polythene Insulation. This dimension is used as the standard size reference for lightweight cables, other types being 1.25" and 1.47"]

Last revised: 19 January, 2022

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