ibiblio
Ibiblio: The Silent War Against the Japanese Navy
Extensive article which chronicles the efforts of U.S. Naval intelligence to read the secret radio messages of the Japanese Navy.
Other
Japan guide.com: Militarism and World War Ii
Outlines Japanese history from 1915-1945. There are also many links to other information about Japan.
PBS
Pbs: American Experience: Pacific Theatre vs. European Theatre
Interview with Stephen Ambrose about the two WWII theatres and Gen. MacArthur's complaints about a lack of funding for the war in the Pacific.