special circumstances. The most immediate risk associated with scuba diving is drowning due to a failure of the breathing gas supply. This may be managed by diligent monitoring of remaining gas, adequate planning and provision of an emergency gas supply carried by the diver in a bailout cylinder or supplied by the diver's buddy. Etymology The word SCUBA was coined in 1952 by Major Christian Lambertsen who served in the U.S. Army Medical Corps from 1944 to 1946 as a physician. Lambertsen first called the closed-circuit rebreather apparatus he had invented "Laru", an (acronym for Lambertsen Amphibious Respiratory Unit) but, in 1952, rejected the term "Laru" for "SCUBA" ("Self-Contained Underwater Breathing Apparatus"). Lambertsen's invention, for which he held several patents registered from 1940 to 1989, was a rebreather and is different from the open-circuit diving regulator and diving cylinder assemblies also commonly referred to as scuba. Open-circuit-demand scuba is a 1943 invention by the Frenchmen Émile Gagnan and Jacques-Yves Cousteau, but in the English language Lambertsen's acronym has become common usage and the name Aqua-Lung (often spelled "aqualung"), coined by Cousteau for use in English-speaking countries, has fallen into secondary use. As with radar, the acronym scuba has become so familiar that it is generally not capitalized and is treated as an ordinary noun. For example, it has been translated into the Welsh language as sgwba. "SCUBA" was originally an acronym, but the term scuba is currently used to refer to the apparatus or the practice of diving using the apparatus, either alone as a common noun, or as an adjective in scuba set and scuba diving respectively. It is also used as an adjective referring to equipment or activity relating to diving using self-contained breathing apparatus. Application A diver uses a self-contained underwater breathing apparatus (scuba) to breathe underwater. Scuba provides the diver with the advantages of mobility and horizontal range far beyond the reach of an umbilical hose attached to surface-supplied diving equipment (SSDE). Unlike other modes of diving, which rely either on breath-hold or on breathing gas supplied under pressure from the surface, scuba divers carry their own source of breathing gas, usually filtered compressed air, allowing them greater freedom of movement than with an air line or diver's umbilical and longer underwater endurance than breath-hold. Scuba diving may be done recreationally or professionally in a number of applications, including scientific, military and public safety roles, but