A self-propelled craft capable of carrying personnel and/or passengers while operating underwater, submerging, surfacing and remaining afloat. Internal pressure is normally maintained at or near one atmosphere.
- Tethered submersible – A ethered self-propelled unit capable of carrying personnel and/or passengers underwater. Internal pressure is normally maintained at or near one atmosphere.
- Wet submersible – A non-pressurised, open-hulled submersible at ambient pressure which is self-propelled and capable of ascent and descent, and which allows the divers access to the surrounding environment.