Amphibian Mark IV


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 Siebe Gorman’s Amphibian Mark IV

Date: 17 January 2003


JW. Bech


Siebe Gorman and Co. Ltd



Amphibian Mark IV


Land of origin



Special Note: 



User group

“frogman”/ ‘human torpedos”


Part no:



Working principle

Auto-Add (CMF) 1.1 ltr/min


Gas type



Cylinder volume



Max. cylinder pressure

120 bar


Material of cylinder



Counterlung inspire

On the back


Counterlung exhale



Dive time duration



Operating temperature



Magnetic signature



Weight ready to use in Air



Weight ready to use in water




30 feet


Scrubber material










Scrubber+ Bottle on the chest



Single hose with shutt off valve

 Pendulum Principle





Exhaust valve mounted in front of the wearer.











If you have any information to add this sheet please mail it to References to source and names will always be added!  


Info found: R.H. Davis, Deep Diving and Submarine operations




Info: Photos thanks to Ake Larsson (advertisement Siebe)


  The original Amphibian triple purpose apparatus, i.e. for use in poison gas or under water, consist of a steel cylinder, charged with pure oxygen for depths not exceeding 30 feet; CO2 absorbent chamber, mouthpiece, noseclip, goggles, a streamlined bag, with excess air escape valve; and- for the use under water only- a lead balance-weight at back, jock strap, etc. For use at greater depths, a mixture of oxygen and air, or of oxygen and helium is used in certain proportions according to the depth at which the diver has to work. (note: first trimix dives?) In some cases the gases are in separate cylinders, each with its own reducing valve  set to deliver the gases in correct proportion. In the modified Amphibian apparatus the excess air of exhaust valve is fitted in front of the wearer, over his shoulder, so as to be more readily accessible. While still of the automatic type, like the more remotely placed valve, the new arrangement also enables the valve to be controlled by hand.

In de the model  III the excess air or exhaust valve is fitted in front of the wearer, over his shoulder, as it was modified in the II series, so as to be more readily accessible. While still of the automatic type,like the more remotely placed valve to be controlled by hand.

Because this set was used by frogman there were requirements of easy breathing. All these requirements mean that special care must be given to the design of the breathing set. It must be designed so that the essentially heavy items such as cylinders and reducers do not upset the delicate balance of the frogman, and must give comfortable, effortless breathing in any and every position that the diver may assume. Siebe’s Amphibian MK III and MK IV, Dunlop’s Underwater Swimming Breathing Apparatus (U.W.S.B.A.) and the Admiralty “Universal” are all designed with this end of view. The design of the breathing system is based upon confirmatory work done at the national Institute of Medical Research for the Admiralty by Docters Sands and Paton. (U.P.S. Report  No. 61).
These workers determined the maximum resistance, expressed in terms of millimetres head of water, wich could be tolerated by divers in all positions under water without interference with normal repiration. The ideal for the breathing bag relative to a diver’s ear was named “Eupnoeic depth”, and it was shown how this depth varied with the depth of respiration. By designing the breathing set so that the eupnoic depth is never exceeded under any conditions, the best breathing conditions are obtained.


eupnoeic (adjective) -

1. passing or able to pass air in and out of the lungs normally; sometimes used in combination
"the boy was disappointed to find only skeletons instead of living breathing dinosaurs"; "the heavy-breathing person on the telephone"
Synonyms: breathing, eupneic





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