Jisaburō Ozawa
Vice Admiral Jisaburō Ozawa, commander of the 1st Mobile Fleet, ordered A-Go to begin on 16 April while he concentrated and refueled his forces east of the Philippines. At nightfall on the 17th his ships were spotted by an American submarine some west of Saipan, although Spruance did not receive its report until the early morning of 18 June. Japanese reconnaissance aircraft located Task Force 58 on that afternoon, but the shorter-ranged American aircraft failed to find the Japanese carriers. Ozawa decided to attack on the 19th rather than subject his inexperienced pilots to night landings that they had not trained for and turned south to keep the range from the Americans constant. Spruance had no idea where the Japanese were until a radio transmission from Ozawa was triangulated at a point west of his task force on the night of the 18th. A radar-equipped Martin PBM Mariner patrol bomber discovered the 1st Mobile Fleet at 01:15 on 19 June, but its message was not received for another eight hours due to radio troubles. The early morning searches by the Americans were not successful, but the Japanese had been tracking them continuously since 01:00.