If the earlier movie about the Pearl Harbor attack is somewhat true, we had radar on Hawaii but it was relatively new and the indications were not fully trusted, either they thought they were supply planes, or just didn’t believe what they saw. Radar was really know, though the Brits used it a great deal in 1940 to track and repel the Luftwaffe.
The movie I’m referring to is “Tora, Tora, Tora” which, to me, is a better representation of the attack than the later movie, “Pearl Harbor” (which seems to be a love story with a war thrown in, instead of the other way around).
Remember its a movie! And yes it was new, not fully trusted or understood. We didn’t yet have the experience the Brits had with it. The details of their success might not have even been available to us prior to entering the war.
A fleet of B-17 'Flying Fortress' bombers from the mainland was expected that morning. The approach of the Japanese planes was close to the anticipated approach of the B-17's. It seems unlikely that the Japanese knew of the expected bombers who flew in unarmed and unprepared for battle.
