UK history

The Cave Diving Group (CDG) was established informally in the United Kingdom in 1935 to organise training and equipment for the exploration of flooded caves in the Mendip Hills of Somerset. The first dive was made by Jack Sheppard on 4 October 1936, using a home-made drysuit surface fed from a modified bicycle pump, which allowed Sheppard to pass Sump 1 of Swildon's Hole. Swildon's is an upstream feeder to the Wookey Hole resurgence system. The difficulty of access to the sump in Swildon's prompted operations to move to the resurgence, and the larger cave there allowed use of conventional "hard hat" equipment which was secured from the Siebe Gorman company. The left photograph on the standard diving dress page will give some indication of the scale of operations this entailed. In UK cave diving, the term "Sherpa" is used without a drop of irony for the people who carry the diver's gear, and before the development of SCUBA equipment such undertakings could be monumental operations.

Diving in the spacious third chamber of Wookey Hole led to a rapid series of advances, each of which was dignified by being given a successive number, until an air surface was reached at what is now known as "Chamber 9." Some of these dives were broadcast live on BBC radio, which must have been a quite surreal experience for both diver and audience.

The number of sites where standard diving dress could be used is clearly limited and there was little further progress before the outbreak of World War II reduced the caving community considerably. However, the rapid development of underwater warfare through the war made a lot of surplus equipment available. The CDG re-formed in 1946 and progress was rapid. Typical equipment at this time was a frogman rubber diving suit for insulation (water temperature in the UK is typically 4 °C), an oxygen diving cylinder, soda lime absorbent canister and counter-lung comprising a rebreather air system and an "AFLOLAUN," meaning "Apparatus For Laying Out Line And Underwater Navigation." The AFLOLAUN consisted of lights, line-reel, compass, notebook (for the survey), batteries, and more.

Progress was typically by "bottom walking", as this was considered less dangerous than swimming (note the absence of buoyancy controls). The use of oxygen put a depth limit on the dive, which was considerably mitigated by the extended dive duration. This was the normal diving equipment and methods until approximately 1960 when new techniques using wetsuits (which provide both insulation and buoyancy compensation), twin open-circuit SCUBA air systems, helmet-mounted lights and free-swimming with fins. The increasing capacity and pressure rating of air bottles also extended dive durations.