The sub is a 3 person sub (pilot and 2 passengers), has 3 different battery systems, and the equivalent of a rebreather system for the cabin to give occupants breathable air for 3 days in case of emergency. While it has full freedom of movement, it's not very fast for horizontal trust, so it gets towed by the surface boat which also keeps constant comms (both voice and telemetry). The cool thing is that they can send location to the sub underneath by locating it compared to the boat's GPS location using sonar. After arriving Cocos on the Argos and doing some dives on the first day, the second morning we went for our first dive to 100 meters. The whole thing was almost 2H.
A few pictures below: