CAVE RESEARCH AND PARK SERVICE UNITS IN THE MARIANA ISLANDS
Karst form and distribution greatly affected the nature and progress of the WWII conflict on these islands. On the limestone outcrops, surface water is absent and most caves are oriented along the location of former fresh-water lens positions, such that the only fresh water they contain is from vadose percolation. For soldiers on both sides of the conflict, the water resources were a constant problem, and many caves contain calcite-coated containers of various forms used to gather water. The distribution of hundreds of flank margin caves at various paleo-lens positions created natural defensive bastions which were extensively exploited by the Japanese. Epigenic stream caves, abandoned phreatic lift tubes, and fissure caves were also utilized. Tunnels and concrete were used to integrate these caves into effective defense networks with interlocking fields of fire. The lessons learned about cave use by the Japanese in the defense of the Mariana Islands was utilized later in the war on volcanic islands such as Iwo Jima, where all caves were artificial. The caves of the Marianas today contain numerous military remains, including dangerous unexploded ordinance.