The extension of the Cape to Australia cable beyond Western Australia to South Australia began in 1900. The distance from Cottesloe to Glenelg was 1,525 nm. and the cable was laid by the C. S. Scotia. A Telegraph Office had been opened at Glenelg in 1859 on the first line constructed to Victoria.
Mr. W. Warren, the Australasian Manager for the Company, said in early 1900 that "it was not to be doubted that South Australia would benefit by the development of her commercial relations, especially with South Africa. He regretted that some of the colonies had stood out, but was of the opinion that they would shortly follow South Australia's example because it was apparent to every commercial man that there was an advantage to be gained in the acceptance of a cheaper rate".
There are two aspects:
On 10 April, 1900 a site for the landing of the cable in South Australia was selected near Glenelg, within shelter of the forts. The site was on Crown lands and was granted to the company for use for the purposes of the cable. The documentation and newspapers of the time refer to Glenelg and other places nearby - including Henley Beach, Grange and Semaphore. In the early 1900s, these places were not as defined as they are now. Hence the official reference to Glenelg is maintained here.
On 11 April, 1900 a quantity of sounding gear was shipped and operations were commenced immediately on the departure of the steamer.
On 12 April 1900, the SA Register reported that "the cable-repairing steamer Sherard Osborn, of the Eastern Extension Telegraph Company, would leave Largs Bay Semaphore anchorage on Friday 13 April 1900. Speaking at a luncheon on this vessel on 11 April, Mr. W. Warren stated that now the South Australian and Western Australian Governments had signed the necessary agreement, the steamer would take soundings between here and Fremantle, and thence to Diego Garcia, in connection with the Cape to Glenelg line. The cable would be manufactured immediately and the Company would not lose one moment in completing the work of giving this colony the new communication with South Africa".
In the month of July, many construction activities were commenced:
Construction began during September/October 1900.
2. The Adelaide to Kangaroo Island cable.
The C. S. Britannia laid a 130 nm cable from Adelaide to just off Kangaroo Island. The cable consisted of the shore end and the intermediate cable.
"At 9 o'clock on Tuesday 30 April 1901 a large staff engaged on the Britannia in connection with the laying of the Cape to Grange cable began operations at the Grange. The Britannia stood out a considerable distance and a mile and a half length of cable was placed on a barge and taken within a couple of hundred yards of the beach. It was then affixed to empty barrels and floated ashore where a team of horses dragged it well inland, and it was buried in a trench 21 ft. deep.
Mr. H. W. McPherson, manager of the Eastern Extension Telegraph Company, supervised operations. The Britannia proceeded towards Kangaroo Island in favourable conditions. When the end of the cable is reached, it will be buoyed to await the arrival of another vessel to continue operations to Fremantle.
A few months will elapse before this can be accomplished, but it is thought that the Fremantle section will be completed before the end of the year". (Adelaide Register, 1 May 1901).
3. The Perth to Glenelg section to complete the cable.
At some time during 1901, the Eastern Extension's cable steamer (C. S. Scotia) returned to England. It returned to Perth in January 1902 to complete the cable laying from Cottesloe to Kangaroo Island.
On Thursday, 20 February, the Scotia was in lat. 35.45 deg. and in long. 131.2 deg. She had then paid out 1,149 miles and about 500 miles remained to be done.
In The Advertiser of 17 February 1902:
"The Cape to Glenelg cable will probably be an accomplished fact on 24 February, as the steamer Scotia, which is laying the last section from West Australia to South Australia is due in Adelaide on that day.
The completion of this great undertaking will probably be celebrated at a gathering on the cable steamer, and there will also be an interest attaching to the first messages dispatched over the new line from Adelaide to London. The shore-end of the cable was laid some time ago as far as Kangaroo Island, and it is there that the connection will be made with the wires which the Scotia is at present paying out".
The Scotia picked up the cable off Kangaroo Island and spliced the two ends together. On Saturday 1 March 1902, the cable was available for public business. The line was formally handed over to the Eastern Extension Company by the construction company.
On Sunday night, 3 August 1902, the Adelaide office of the Eastern Extension Telegraph Company spoke direct with London over the new Cape-Grange line and received a reply in three minutes.