The battle of the Coral Sea was historically significant as the first action in which the opposing fleets neither sighted nor fired upon one another.
Having broken the Japanese naval code. Nimitz knew that the Japanese would soon launch Operation MO in the South Pacific, to seize the Solomons and Port Moresby on the southeastern coast of New Guinea. If successful, these conquests would gravely threaten Australia. Based on this intelligence, He send the Lexington task force, then in Hawaiian waters, to reinforce Fletcher’s Yorktown task force in the Coral Sea. And so began the first Carrier Battle in History.