When Eldred decided that rebreathers were not suitable for general sport use, he shifted his focus to developing the world's first single-hose open-circuit scuba set, both with tradename "Porpoise".

At a demonstration by the Flinders pier, on Western Port Bay, south east of Melbourne, a diver passed out because he failed to purge the system of air.

Eldred realised at this point that he needed to turn his efforts toward open circuit compressed air breathing apparatus.

The French-designed open circuit scuba, called the Aqua-Lung, was protected by US and international patents, so Eldred set about designing the Porpoise CA (a prototype), the world's first single hose regulator.

The Porpoise single hose scuba found its initial international praise in Arthur C. Clarke's 1955 book Coast of Coral.

[5] Clarke brought two French Mistrals to Australia, but set them aside when he was loaned two Porpoises for his Australian adventure by Eldred.

Eldred's company was called Breathing Appliances Pty Ltd and located at 70 Abbotsford St., North Melbourne.

The Royal Australian Navy (RAN) supported Eldred's efforts and adopted the Porpoise Universal for military use.

Eldred's diving school was established by RAN Commander Maurice "Batts" Batterham, GM.

[4] It was the first SCUBA diving school in Australia and the first in the world to teach with the single hose regulator — it was located at the Melbourne City Baths.

The school continued for about ten years, later sending its students to the newer Associated Divers Academy which taught at the YMCA.

Later Australian Divers Spiro ceased production of all of the Porpoise models, but had to continue to supply the RAN because of an existing contract.

Ted Eldred was recognised in later life, by the Historical Divers Society (South-East Asia Pacific), as the inventor of the first successful commercially produced single hose SCUBA.

Ted Eldred died of cardiac arrest at his Yarck, Victoria country home, in August 2005.