Where did the Island Hopping Campaign (WWII) start at?

Were ships and planes sent out from the actual United States, or were they sent out from various islands located in the Pacific? I ask because I need a 'hook' for my presentation, and I wanted to say something along the lines of: "The west coast of the U.S. is 5000 miles away from Japan. Unfortunately, Japan just gained control of the Pacific waters. How would it be possible to make it to Japan without being sunk or shot down?". The only problem with this is that I don't know if in fact planes and ships were sent from the actual U.S. mainland. Anybody know? Thanks.