Answer: Self Contained Underwater Breathing Apparatus.

A common misconception is that Jacques Cousteau coined the term. Though he did create the first “Aqualung” in 1943, it took over a decade for the acronym SCUBA to take off. SCUBA was first coined by Dr. Christian Lambertsen of the University of Pennsylvania Medical School in 1954. He was in the process of creating the first rebreather prototypes for military frogmen. Lambertsen is also responsible for breakthroughs in decompression theory and mixed-gas breathing!