Before and After

Japan had a very strategic plan building up before they went to attack America.

Pearl Harbor. Of all the aspects of the attack on that 7 December 1941 Sunday morning-including its treachery, swiftness, daring, and skillful execution-none seems more compelling than the assault's total surprise. This element is even more striking, knowing that just prior to the attack, a U.S. Army radar site at Opana Point, on Oahu, tracked incoming aircraft, and the Navy discovered a foreign submarine at the entrance to Pearl Harbor. Add to this mixture that American code-breakers were reading Japanese diplomatic messages of all types, and it seems simply incredible that Japan could pull off a thorough surprise attack. -Hanyok

The reason Japan was able to keep their plan hidden from the U.S is because of all the plans they took carefully to execute their plan. They spent a while studying American broadcast signals to wait for the perfect time to attack. They were also covering up their tracks to their plans.