Monday, May 4, 1942. The Battle of Coral Sea commences.

Today in World War II History—May 4, 1942: Battle of the Coral Sea begins: US Navy intercepts Japanese fleet set to invade Port Moresby, New Guinea: first carrier vs. carrier battle in history.

It was, as noted, the first carrier task force v. carrier task force naval engagement in history, and the first engagement between two fleets in which the opposing forces never had visible surface engagement with each other.  It would run until May 8, and result in more US losses than Japanese ones, but it would frustrate Japanese attempts to take Port Morseby and therefore was an American strategic victory.  Indeed, it was the first time in the war that the Japanese had to withdraw without achieving their objective.