The Battle of Leyte Gulf
Naming the largest naval battle in history depends on the definitions of "largest" and "battle." Potential criteria include number of people and ships involved, the total tonnage of vessels, the size of the battlefield, and the duration of the fight. There are three main candidates, each of which are said to have involved about 200,000 personnel: the Battle of Salamis, the Battle of Ecnomus and the Battle of Leyte Gulf.
The first two occurred in the Classical Era, when ancient sources frequently exaggerated the numbers involved in warfare. For example, Herodotus claimed in The Histories that Xerxes invaded Greece with some 2,600,000 soldiers, but it is commonly believed that only 100,000-200,000 troops actually participated. Since Herodotus is one of the key sources for information on the Battle of Salamis, it is likely that it involved far fewer than the claimed 200,000 sailors and 1,642 vessels. Figures for the Battle of Ecnomus are similarly dubious. In contrast, the Battle of Leyte Gulf was fought during World War II, and one side was fielded by liberal democracies, with strong record-keeping institutions.