The Battle of the Coral Sea was important because it thwarted the Japanese attempt to invade Port Moresby in New Guinea, depriving them of a secure zone between Japan and Australia. According to History.com, it was also the first air-sea battle in history in which planes launched from aircraft carriers at sea played a vital role.
Due to successful attempts to break Japanese code, the Allies had advance warning of the Japanese invasion of Port Moresby. After damaging a seaplane base on Tulagi in the Solomon Islands, an Allied fleet led by Rear Admiral Frank J. Fletcher rushed to the Coral Sea. Japanese aircraft damaged and sank the destroyer USS Sims and damaged the oiler USS Neosho. In turn, Allied aircraft sank the Japanese aircraft carrier Shoho and badly damaged the carrier Shokaku. The American carrier USS Lexington was hit repeatedly by bombs and torpedoes, caught fire and was sunk to avoid capture. Eventually, the Japanese commander ordered the invasion fleet to retreat.
Both sides suffered heavy losses. Besides the ships sunk and damaged, 543 Allied forces and 1,074 Japanese forces were killed. The Allied effort blocked the offensive of the Japanese in the South Pacific and impacted the result of the subsequent Battle of Midway, which significantly damaged the Japanese carrier fleet and caused the war initiative to pass to the Americans.