What warning could have changed at Pearl Harbor

Would the radar alert and submarine sighting have made a major difference if taken seriously?

Radar likely could have enabled fighters to launch; the submarine sighting probably reached the right commanders too late.

The answer separates different forms of warning rather than treating them as interchangeable. A radar contact could reach air-defense decision-makers quickly enough to launch some fighters and man guns. The submarine sighting had to pass through a slower reporting and command chain before it could change base-wide readiness. Both reports mattered, but they offered different amounts of usable time to different commands. The lesson is that warning only becomes defense when a communications system converts detection into orders before the threat arrives.