Advice on Diving in Northern Mariana Islands

...ts.  Only the islands of Saipan, Rota, and Tinian are permanently inhabited and the diving is considered some of the best in the world.  There are beautiful coral reefs dotted with tropical fish; the sunken ships and other relics of World War II; and stunning caverns and caves perfect for underwater photography.  The diving is diverse, but always has warm waters and great visibility.  Ranging over 400 nautical miles, the southern limestone islands are surrounded by fringing coral reefs and the northern islands are volcanic with three still actively volcanic.  There are three paved airport run...