Engadget recently reported on Britain’s used of the Isis ROV unmanned sub to explore the depths of Antarctica.  There are other unmanned subs used to explore the depths of the oceans.  National Geographic and Woods Hole National Oceanographic Institute use REMUS.  UUV (Unmanned under water vehicles) are also used by the Navy for defense reasons.  Other unmanned submersibles can be found at NOAA Ocean Explorer. 

And if YOU want to go down to 1500 feet check out the DF-502.  For a price, the company will train you for an underwater pilot’s license.