Deployed from San Diego to the Hawaiian Territory in May 1940, the American fleet boasted impressive aircraft carriers and battleships. The move brought U.S. naval power closer to British interests.
President Roosevelt sent a secret memo, dated June 30, 1940, instructing an aid to get a message to Churchill. In it FDR expresses his opinion that having the fleet in Hawaii is "vital." Not everyone (like Admiral James Richardson) agreed the fleet would be safe there.
Strategically located between the U.S. mainland and East Asia, Pearl Harbor is a naturally protected safe haven. With eight of America’s best battleships lined up along Ford Island and numerous other ships scattered throughout the harbor, it was an impressive sight. Several aircraft carriers also called Pearl Harbor home. So did planes based at Hickam Field.
Yamamoto wanted to destroy that impressive array. He assigned "Operation Hawaii" (code-named "Operation Z") to his able assistant, Lt. Commander Minoru Genda who suggested the use of massed aircraft carriers instead of battleships.
The Pearl Harbor attack plan was ready by October 31, 1941. It was amazingly similar to the "Martin-Bellinger Report," prepared by two Americans during the spring of that year. Assigned to assess U.S. vulnerabilities at Pearl Harbor, General Martin and Admiral Bellinger made the following observation on March 31, 1941 (in the "Possible Enemy Action" section):
In a dawn air attack, there is a high probability that it could be delivered as a complete surprise in spite of any patrols we might be using and that it might find us in a condition of readiness under which pursuit would be slow to start...
Both sides had assessed identical risks. But there was something more in the on-target report. Referring to Japan as "Orange," the report stresses:
In the past Orange has never preceded hostile actions
by a declaration of war.