The PCBU or Pressurized Cavity for Breathing Underwater (PCBU) is a cabin fitted with a opening at the bottom which can be used by divers without diving gear with incorporated compressed air tank (SCUBA) or surface supplied diving gear. The cabin hence works as a underwater cavity filled with air (moon pool) in which the divers can catch breath and then continue work underwater. Alternatively, it can also be used to work in (ie for planting coral on coral tables, reef balls, ...). The PCBU can be used for this at depths upto 8m (below this decompression sickness can occur.
The PCBU is fitted with a compressor and umbilical cord that can be sent upto the surface (using 2 balloons, atleast when inflated). The compressor generates compressed air and sents it into the cavity when the PCBU is deployed (when deployed, the yellow hatches are attached and the PCBU is fixed to the seafloor). The compressed air tank is also filled by the same compressor and stores air for the diver (which controls the device when it needs to be moved)
The device is not intented to be propelled over large distances however; instead it is envisioned to be carried by a boat and when the boat has about come to the work location, the PCBU is propelled using it's own propeller. It can not be propelled anymore when deployed. See the 'Purchasing_the_models' link at appropedia's AT_CAD_Team for additional information on the model