Members of the RN and RM who volunteered as Ship's Divers underwent a one-day aptitude test, concentrating on swimming ability, fitness, an ability to work under pressure and suitability for diving.
Those selected from the apptitude (and many diddn't make the grade) went on an intensive four-week course, which consisted of compressed air (open-circuit) diving.

There was also extensive instruction (and practice) on searching ships bottoms for explosives, as well as instruction in working on ship's hulls, decompression chambers and maintenance of diving equipment.
On completion, the diver returned to his ship or shore establishment and to maintain their qualification (and get their diving pay) were required to dive for at least 120 minutes during each four-month period.