Finally, someone who is really into the history of what happened! Part of the problem was confusion over the USS Ward "attacked what they thought was a sub" or "Attack and definitely sunk a sub". The command thought that the message sent meant the first meaning and not the second meaning. Before notifiying anyone, they were trying to figure out what the heck was going on outside the harbor. Steps were taken; the ready duty destroyer, USS Monaghan was notified at 7:51 to join Ward and to check the area. The Japanese air attack then began at 7:55.

Even being the "ready duty" destroyer, Monaghan was underway in the channel until 8:27, 36 minutes after being notified. The main failure was that the Ward attacked and sank the sub at 6:45. It took roughly an hour for the message to get from Ward to various commands to Monghan.

So the question is, how much difference would an hour's warning have made? It took the ready duty destroyer 30 minutes, and thats with the ship being in a partial status of readiness. The ship had more broilers ready and limited crew on shore leave. The other destroyers and cruisers were in a lessor state of readiness, some taking hours to get out.

The battleships were another story. Most of them were in various stages of readiness (California had the double bottom open, Pennsylvania in drydock, Tennessee and Maryland moored inbound of other ships) were all out of the running for a quick sortie. Of the remainer, all of them had only one broiler running to provide the ship power, except for Nevada. It took hours to get them all going; so the fact that Nevada happened to have 2 going at once as they were switching over was luck. Thats why it was the only battleship to make way during the attack.

Most of the pilots from the Army Air Corps and Naval Station were all on leave. There were no cell phones... so the one hour difference would not have put many planes in the air, and the few that were would not have had the oppertunity for a coordinated defense. They would have been a mixed bag or random pilots from random bases and squadrons in the air, with mixed leadership.

The biggest thing that would have been different were the number of manned guns. In the first wave they lost 9, using the element of surprise. In the second wave, facing an alert harbor they lost 20. They launched 403 aircraft total, so even if they had lost 20 and 20, the loss of 40 aircraft would not have changed the outcome.

Even if by miracle, FDR found out the Japanese were heading for Pearl, and the fleet had 3 hours to move all the ships out and attack, it would have been a disaster. The Japanese submarine screen would have spotted them and broke radio silence to alert the fleet. The battleships make only 23 knots and the japanese planes have a range of hundreds of miles. It would have looked like a GB with 8 BB1s and some CAs/CLs taking on 6 CV5s on a massive map. The BBs would never get their guns withing the 15,000 meters needed to shoot with a speed disadvantage of about 10 knots. Instead of hitting the land targets, the japanese fleet would have concentrated on the ships, not the land, and the ships sunk would have been lost at the bottom of the ocean instead of the bottom of the harbor. Land based air power at pearl was mostly fighters, so they would have had no ability to damage the fleet. Further, the fighters traveling out to sea and back would then have limited ability to stay over the BBs for limited time provide cover. What could the cruisers and DDs of Pearl Harbor have done to the japanse fleet is uncertain. They never found it on December 7th, so its likely in this senario that they would have either.

The best thing that happened to the fleet was staying in the harbor and fighting there. I do wonder what the battle would have looked like if all those USN DDs, CLs, and CAs had encountered the IJN fleet with its limited screen.