When he heard explosions outside his home on the north rim of Pearl Harbor, 71 years ago this week, young Walter T. Oka’s first thought was: “The Army was mad at the Navy.”

He rushed outside to see what was going on, and continued to believe the attack on the Pacific Fleet moored at Pearl Harbor was a training exercise until he spotted “the meatballs” — the colloquial term for Japan’s rising sun insignia — on the attacking planes.