Davis Submerged Escape Apparatus The Davis Submerged Escape Apparatus ( also referred to as DSEA ) , was an early type of oxygen rebreather invented in 1910 by Sir Robert Davis , head of Siebe Gorman and Co . Ltd . , inspired by the earlier Fleuss system , and adopted by the Royal Navy after further development by Davis in 1927 . While intended primarily as an emergency escape apparatus for submarine crews , it was soon also used for diving , being a handy shallow water diving apparatus with a thirty minute endurance , and as an industrial breathing set . Design . The DSEA rig comprises a rubber breathing / buoyancy bag , which contains a canister of barium hydroxide to scrub exhaled CO and , in a pocket at the lower end of the bag , a steel pressure cylinder holding approximately 56 litres of oxygen at a pressure of 120 bar . The cylinder is equipped with a control valve and is connected to the breathing bag . Opening the cylinder ' s valve admits oxygen to the bag and charges it to the pressure of the surrounding water . The canister of CO absorbent inside the breathing bag is connected to a mouthpiece by a flexible corrugated tube ; breathing is carried out by the mouth only , the nose being closed by a clip . Goggles are also provided as a standard part of the apparatus . The breathing / buoyancy bag is fitted with a non - return release valve which allows air to escape from the bag as the user ascends towards the surface and the water pressure decreases . The wearer can close this valve on reaching the surface , the air in the breathing / buoyancy bag then serving as a life preserver . If the bag becomes deflated while the wearer is on the surface awaiting rescue , it can be refilled ( for use as a lifejacket ) by opening the non - return valve and blowing through the mouthpiece . The usual Royal Navy DSEA rig also included an emergency buoyancy bag on the front of the main breathing / buoyancy bag to help keep the wearer afloat after reaching the surface even if he had exhausted the air in the breathing / buoyancy bag . This emergency bag was inflated by an " Oxylet " canister inside it - a small steel oxygen cylinder which was opened by breaking its weakened neck and wrenching sharply . It also had a speed - retarding drogue , which was a rubber apron unrolled and held out horizontally by the wearer as he ascended , dramatically reducing his speed of ascent through water resistance . Operational service . The Davis Submerged Escape Apparatus was the first or nearly the first rebreather to be made in quantity . Adopted by the Royal Navy in 1929 , DSEA was used with limited success to assist crew members to escape from several sunken submarines , for example HMS " Poseidon " in 1931 , HMS " Thetis " in 1939 and HMS " Perseus " in 1941 . A small version of the DSEA , the Amphibious Tank Escape Apparatus ( ATEA ) was produced for use by the crews of amphibious DD tank s such as those used during the Normandy landings . There were instances , mostly during WWII , of the DSEA being used for swimming down from the surface , i . e . for early scuba diving . In WWII it was also notably used by the Underwater Working Party at Gibraltar led by Lt . Lionel " Buster " Crabb , and worn at times by frogmen piloting ' Sleeping Beauty ' Motorised Submersible Canoe s .