Rio de Janeiro Maru
At the time of her requisitioning by Japanese Naval forces in 1940, 460 ft long Rio de Janeiro was a 9300 tons eight-deck passenger liner that had a crew of 150 people and could carry over thousand of passengers. Navy obviously did not have a use for a passenger liner, and Rio was converted into a submarine tender.
As other victims of operation Hailstone, Rio was sunk on Feb 18, 1942. Today, it can be found laying on the bottom on its starboard side, with the sand at about 110 ft. Two very nice propellers are still in place in between 80 and 100 ft deep. The port side comes to about 40 ft and can be an exiting place to do a twilight or a night dive.
Highlights are numerous and include massive and very photogenic stern gun (below are the view from above); bottles of sake in the hold closest to stern; already mentioned props; very interesting companionways with some spare submarine parts lining the floors.
Hazards deal with penetration and length. Because of its position, it can be disorienting inside and some compartments are collapsing rapidly. It is also can become quite long if you spend too much time admiring the stern attractions and your boat is moored to the bow.