In 1951, the British Post Office evolved an entirely new type of deep-sea submarine telephone cable which was intended to overcome many of the serious disadvantages inherent in conventional wire-armoured cable. This new cable, known as the Lightweight cable because of its very light weight in water, was under exhaustive development for seven years before it could be accepted with confidence for a trans-ocean system. 1600 miles of this cable have now been laid on the Anglo-Canadian (CANTAT) system, and in all respects it has met the highest performance expectations. It has also proved to be much cheaper than a comparable conventional cable. Its electrical stability is noteworthy as it has exhibited a much smaller attenuation laying change than that experienced with previous cables, and, during the first year, there has been no significant indication of ageing. This type of cable is expected to be employed on all new deep-sea systems.