While Japanese felt elated by the news of victories in the South, Japanese mainland was attacked from the air on April 18th, 1942. Sixteen B25 bombers led by Lieutenant Colonel Doolittle took off from aircraft carrier 'Hornet' and attacked the area among Tokyo, Aichi and Hyogo.
It happened when Japanese headquarter planed to isolate Australia by attacking Port Moresby, New Guinea and then occupy Midway and attack Aleutian Islands. The mainland attack made Imperial Navy, led by commander-in-chief of the Combined Fleet Yamamoto, to target aircraft carriers of US Pacific Fleet again.
Battle of the Coral Sea
Japanese army, which held naval dominance over the South by destroying Britain's Eastern Fleet, planned to conquer Port Moresby, New Guinea to disable coordinated strategy between Australia and US. The plan was called 'MO operation'. Imperial navy organized a mobile unit of two aircraft carriers and one light aircraft carrier to guard the attacking unit.