Thirty minutes could activate Pearl Harbor's defenses

How useful would thirty minutes of reliable warning have been at Pearl Harbor?

It could not stop the raid, but it could put fighters and some bombers in the air while activating radar, guns, and shipboard readiness.

The warning mattered across the whole defense rather than only to a single informed person. Fighters could begin launching, radars and antiaircraft defenses could be fully manned, and some B-17s might be armed for an improvised search or strike. Battleships could also begin creating more separation along Battleship Row. None of these measures guaranteed interception, but they would make the attackers face an alert base instead of a cold start.