Why couldn't the US detect the Japanese when they bombed pearl harbor?

Answer 1

The Japanese fleet was thought by most intelligence officers to be near the Philippine Islands. They sailed with complete secrecy and in total radio silence, avoiding all major shipping lanes and fishing areas. The attack position they settled on was not in the line of any aircraft corridors, and they were therefore able to avoid detection completely.

Perhaps adding to the problem was that although the American generals and admirals on Hawaii had been placed on alert, they did little to increase patrols with submarines and aircraft. General Short and Admiral Kimmel were severely reprimanded after the attack.