There were five US Army mobile air search radars of the SCR-270B model on Oahu. They were delivered two weeks before December 7th 1941. The one at Kahuku Point was being operated by two privates, who were due to go off duty at 7 am. Since radar was so new, they decided to operate the radar a little while longer. At 7:02 am, they detected a huge formation of planes, 137 miles away and flying towards Oahu. At first they thought their radar was broken, because they never saw a blip that big before. By 7:09am, they could find no problems with their radar and called Fort Shafter to make a report. Nobody with any authority was at the desk on Sunday morning. It took six minutes to find an officer, Lieutenant Kermit Tyler, who did call the two privates back. He heard their report and dismissed it. The young lieutenant knew a formation of B-17 bombers were due to land at Hickam airfield at 9 am and just assumed that the "big blip" the radar saw were these B-17s. It was 7:20 am when Lt Tyler told them to "Don't worry about it."
This was 35 minutes before the attack started. Even if Lt. Tyler notified all of the Army air fields on Oahu by 7:30, there is a questionable doubt if a peace-time Sunday morning drill would have made much of a difference. Perhaps twenty to thirty fighters could have taken off. They would have shot down more than the 29 planes the Japanese really did lose in the Pearl Harbor attack, but they would not have stopped the attack.
The US Navy destroyer Ward found and sank a Japanese miniature submarine shortly before 6 am and the USS Ward did report this action. The Officer on duty at the Pearl Harbor Navy Yard dismissed it and thought the destroyer just depth charged a whale.
Source "At Dawn We Slept" by Gordon Prang