The Battle of the Philippine Sea (June 19--20, 1944)
The largest aircraft carrier battle in history, the largest single naval battle of World War II, and arguably the largest in history, involving 15 US fleet and light carriers, nine Japanese carriers, 170 other warships and some 1,700 aircraft. The US Fifth Fleet's Task Force 58 is (in terms of tonnage) the largest single naval formation ever to give battle.
The Battle of Leyte Gulf (October 23--26, 1944)
The largest in terms of tonnage of ships in the combined orders of battle, if not necessarily in terms of tonnage of the ships engaged. Also the largest in terms of the tonnage of ships sunk, and in terms of the size of the area within which the component battles took place. The United States 3rd and 7th Fleets, including some Australian warships, comprised 8 large aircraft carriers, 24 light/escort carriers, 12 battleships, 24 cruisers, 141 destroyers, many other ships, and around 1,500 aircraft. They won a decisive victory over Japanese forces, which consisted of four aircraft carriers, nine battleships, 19 cruisers, 34 destroyers and several hundred aircraft. The opposing fleets carried a total of about 200,000 men. Leyte Gulf consisted of four major subsidiary battles: Battle of Sibuyan Sea, Battle of Surigao Strait, Battle off Samar and Battle of Cape Engano, along with other actions. These are counted together by virtue of their all being caused by the Japanese operation Sho-Go, which was aimed at destroying the Allied amphibious forces involved in the invasion of Leyte. However, the individual battles were separated by distances as great as two hundred miles.