The Marianas were heavily defended .
In order to set up forward air bases capable of supporting operations across the mid-Pacific , to the Philippines , and into Japan , the U.S. planned to take the Mariana Islands .
The Mariana Islands were heavily defended .
In order to set up forward air bases capable of supporting operations across the mid-Pacific , to the Philippines , and into Japan , the U.S. planned to take the Mariana Islands .