In response to the invasion, the Japanese launched their final major naval effort, an operation known as 'Sho-Go', involving almost all their surviving fleet. It was aimed at destroying the invasion shipping in the Leyte Gulf. The Northern Force of Admiral Ozawa was built around the remaining Japanese aircraft carriers, now weakened by the heavy loss of trained pilots. The Northern Force was meant to lure the covering U.S. forces away from the Gulf while two surface battle-groups, the Center Force and the Southern Force, were to break through to the beachhead and attack the invasion shipping. These forces were built around the remaining strength of the Japanese Navy, and comprised a total of 7 battleships and 16 cruisers. The operation brought about the Battle for Leyte Gulf, the largest naval battle of the Second World War and, by some criteria, the largest naval battle in history.