By then, American radar had detected the incoming Japanese planes, and the U.S. commander immediately launched all the available planes based at Midway. The planes took off, some to intercept the Japanese planes, others to evacuate. The radar -- one thing that the US had, that the Japanese did not -- produced critically decisive results. It gave the US a distinct advantage in discovering an enemy position. Without radar, the Japanese had to rely on visual observation to locate the enemy.
Japan had a second flight group on their carriers. Of those 108 aircraft, the dive bombers were armed with general purpose bombs, the fighters armed with torpedoes. Akagi's headquarters, having just received the message and not yet having any reports of the enemy carriers, decided to launch a follow-up strike on the American base, and ordered to change the armament on all the aircraft to "land" bombs.
However, just as they had given the order to rearm the aircraft, a Japanese scout plane reported it had spotted the enemy. Another message indicated there was an American carrier with the enemy formation previously identified. The headquarters decided to reverse the rearming operation, judging that the enemy was still far away and that the armament would have been ready in time for an attacked to be launched.
Rear Admiral Tamon Yamaguchi, Commander of the Second Carrier Division, stepped in to urge the flagship that a strike be launched immediately against the American carrier regardless of the armament condition, as he feared that the danger was imminent. However, this suggestion was declined.