Porpoise is a tradename for scuba

Scuba set

A scuba set is an independent breathing set that provides a scuba diver with the breathing gas necessary to breathe underwater during scuba diving. It is much used for sport diving and some sorts of work diving....

 developed by Ted Eldred

Ted Eldred

Edward Francis Eldred was a pioneer of scuba diving in Australia. He invented the Porpoise .-Early years:...

 in Australia

Australia

Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

 and made there from the late 1940s onwards. It included:

A make of diving oxygen rebreather

This rebreather

Rebreather

A rebreather is a type of breathing set that provides a breathing gas containing oxygen and recycled exhaled gas. This recycling reduces the volume of breathing gas used, making a rebreather lighter and more compact than an open-circuit breathing set for the same duration in environments where...

 was developed by Ted Eldred

Ted Eldred

Edward Francis Eldred was a pioneer of scuba diving in Australia. He invented the Porpoise .-Early years:...

 in the late 1940s and early 1950s. Some were made and used for sport diving, but they did not go into full production. It was worn on the back without a casing. The bag was between the canister and valve assembly and the diver's back. It had two wide breathing tubes like an aqua-lung

Aqua-lung

Aqua-Lung was the original name of the first open-circuit free-swimming underwater breathing set in reaching worldwide popularity and commercial success...

 or an IDA71, running to a mouthpiece

Mouthpiece (scuba)

In breathing sets, a mouthpiece is a part that the user grips in his mouth, to make a watertight seal between the breathing set and his mouth. It is composed of a short flattened-oval tube that goes in between the lips, with on its free end a flange that fits between the lips and the tooth and gums...

, which had a shutoff button to keep water out when it was not in the mouth. It appeared in three versions: MK1, MK2, MK3. It had a special valve that both breathing tubes ran through: it was activated by surrounding pressure; when he got deeper than was safe for pure oxygen it restricted (not stopped) the supply of breathing gas, to tell him to go to shallower depth. (Before open-circuit scuba was readily available in Australia, many Australian sport divers used war-surplus Siebe Gorman Salvus

Siebe Gorman Salvus

The Siebe Gorman Salvus is a light oxygen rebreather for industrial use or in shallow diving. Its duration on a filling is 30 to 40 minutes. It was very common in Britain during World War II and for a long time afterwards...

es.)
porpoise pictures

A make of single-hose open-circuit scuba

For more information see Ted Eldred#Open-circuit.

This was the first single-hose open-circuit scuba

Scuba set

A scuba set is an independent breathing set that provides a scuba diver with the breathing gas necessary to breathe underwater during scuba diving. It is much used for sport diving and some sorts of work diving....

 made in the world. Ted Eldred

Ted Eldred

Edward Francis Eldred was a pioneer of scuba diving in Australia. He invented the Porpoise .-Early years:...

 in Melbourne

Melbourne

Melbourne is the capital and most populous city in the state of Victoria, and the second most populous city in Australia. The Melbourne City Centre is the hub of the greater metropolitan area and the Census statistical division—of which "Melbourne" is the common name. As of June 2009, the greater...

 in Australia started designing it in 1948 to "design around" the Cousteau-Gagnan aqua-lung

Aqua-lung

Aqua-Lung was the original name of the first open-circuit free-swimming underwater breathing set in reaching worldwide popularity and commercial success...

 patent, and to get rid of air supply restrictions that affected early Cousteau-Gagnan-type aqua-lungs. He started making it commercially in 1952. The Royal Australian Navy

Royal Australian Navy

The Royal Australian Navy is the naval branch of the Australian Defence Force. Following the Federation of Australia in 1901, the ships and resources of the separate colonial navies were integrated into a national force: the Commonwealth Naval Forces...

 adopted it. It was the origin of single-hose scuba regulators. It was much used by Australian scuba divers. The picture shows the CA-1, a set with one cylinder

Diving cylinder

A diving cylinder, scuba tank or diving tank is a gas cylinder used to store and transport high pressure breathing gas as a component of a scuba set. It provides gas to the scuba diver through the demand valve of a diving regulator....

 with its valve at the bottom, strapped directly to the back with rucksack-type straps without backpack plate or buoyancy aid, with a single-hose regulator

Diving regulator

A diving regulator is a pressure regulator used in scuba or surface supplied diving equipment that reduces pressurized breathing gas to ambient pressure and delivers it to the diver. The gas may be air or one of a variety of specially blended breathing gases...

-mouthpiece which could be strapped in. The tank was inverted so that the diver could reach the regulator mounted reserve handle. The head strap was intended to keep the demand valve from falling well below the diver, if dropped from the mouth. The high-pressure regulator screwed into the side of the cylinder

Diving cylinder

A diving cylinder, scuba tank or diving tank is a gas cylinder used to store and transport high pressure breathing gas as a component of a scuba set. It provides gas to the scuba diver through the demand valve of a diving regulator....

 valve like welding equipment of today; there was no A-clamp. Versions of it were made for the Australian Navy until 1976, and the last one known to be sold to the public was sold in that year. About 12,000 Porpoise units of all models were produced. About 50 Porpoises still exist. Only a few of these early models are known today, the rarest being the CA-2, made for use with two tanks.