Actually, there are almost no deep diving submersibles left in service. They have been almost completely replaced by tethered "robots" (actually remote control

Actually, there are almost no deep diving submersibles left in service. They have been almost completely replaced by tethered "robots" (actually remote controlled vehicles) in scientific and industrial (oil, pipeline, and cables) use because they are much cheaper and can do all the observation and light collection that submersibles used to do. Unfortunately, they are also less flexible.