The Battle of the Coral Sea was a very significant turning point in the battle of the Pacific because of the effects on attacking Japanese weaknesses, the effects on Port Moresby, and the effects on the Battle of Midway. Before this battle, every time the two fleets clashed, both were able to see their enemy. The Battle of the Coral Sea was the first time that two fleets clashed, and that neither fleet saw each other. The Battle was also significant because it was fought entirely with aircraft. The Battle of the Coral Sea marked the first strategic defeat of the Japanese Imperial Navy.
The reason that the Battle of the Coral Sea came about was because the Japanese were intent on capturing Port Moresby, New Guinea. Japanese preparations for the occupation of Port Moresby were underway by April. The invasion itself was planned for March, but the appearance of the United States carrier forces in the south-west Pacific had postponed it until May. This attack was called Operation "MO" and if Japanese managed to take Port Moresby they would have a full control over the Coral Sea and they would cut Australia out of the war.
Some have argued that the Battle of the Coral Sea began on April 28, 1942 when the Japanese began building a seaplane base in Shortland in the Solomons. This would enable four-engine flying boats to begin long-range patrols the next day. However, the actual fighting between the Japanese and American carrier groups lasted from May 4 to May 8.
The American forces consisted of Task Force 17, which centered around the carrierYorktown and Task Force 11, centered around the carrier Lexington. Task Force 11 was led by Rear Admiral Aubrey Fitch while Task Force 17 was led by Rear Admiral Frank Jack Fletcher, who would later take over command for both Task Forces. Task Force 11 had 69 planes, two heavy cruisers, and six destroyers, while Task force 17 had 67 planes, three heavy cruisers, six destroyers, and two fleet oilers.
The Japanese forces were coordinated by Vice Admiral Shigemi Inoue, who was given free reign by Admiral Isoroku Yamamoto, commander of the combined fleet. Inoue had at his disposal in the Battle of the Coral Sea the powerful MO Striking Force under Takeo Takagi, which consisted of a troop convoy and a close escort force of the light carrier Shoho, along with the 5th Carrier Division led by Chuichi Hara and the Tulagi Invasion Force under Kiyohide Shima. The 5th Carrier Division had the large carriers Shokaku and Zuikaku. By the time that the dust had settled between these two heavy weights, the Japanese had lost the light carrier Shoho, suffered damage to the Shokaku so that it could not launch or receive any planes, and had lost a destroyer and several auxilaries. Also the Japanese were reduced to only 39 aircraft. The Americans on the other hand had suffered the loss of the Neosho, a fleet oiler, the Sims, a destroyer, and the Lexington, a carrier. Oddly enough, the Americans were also left with 39 aircraft. The Americans had, in effect, won a strategic battle. They had stopped the Japanese advance on Port Moresby as Inoue had to postpone the invasion indefinitely. The Battle of the Coral Sea would also have further implications on American and Japanese strategy in the Pacific as well as effects on the Battle of Midway.