United States Third Fleet in the context of Numbered fleet

USS Iowa (BB-61) is a retired battleship, the lead ship of her class, and the fourth in the United States Navy to be named after the state of Iowa. Owing to the cancellation of the Montana-class battleships, Iowa is the last lead ship of any class of United States battleships and was the only ship of her class to serve in the Atlantic Ocean during World War II.

During World War II, she carried President Franklin D. Roosevelt across the Atlantic to Mers El Kébir, Algeria, en route to a conference of vital importance in 1943 in Tehran with Prime Minister Winston Churchill of the United Kingdom and Joseph Stalin, leader of the Soviet Union. When transferred to the Pacific Fleet in 1944, Iowa shelled beachheads at Kwajalein and Eniwetok in advance of Allied amphibious landings and screened aircraft carriers operating in the Marshall Islands. She also served as the Third Fleet flagship, flying Admiral William F. Halsey's flag at the Japanese surrender in Tokyo Bay.

The Battle off Samar was the centermost action of the Battle of Leyte Gulf, one of the largest naval battles in history, which took place in the Philippine Sea off Samar Island, in the Philippines on October 25, 1944. It was the only major action in the larger battle in which the Americans were largely unprepared. After the previous day's fighting, the Imperial Japanese Navy's First Mobile Striking Force, under the command of Takeo Kurita, had suffered significant damage and appeared to be retreating westward. However, by the next morning, the Japanese force had turned around and resumed its advance toward Leyte Gulf. With Admiral William Halsey Jr. lured into taking his powerful Third Fleet north after a decoy fleet and the Seventh Fleet engaged to the south, the recently landed 130,000 men of the Sixth Army were left vulnerable to Japanese attack on Leyte.

Kurita, aboard the Japanese battleship Yamato, took his large force of battleships, cruisers and destroyers from the San Bernardino Strait and headed south toward Leyte, where they encountered Task Unit 77.4.3 ("Taffy 3"), the northernmost of the three escort carrier groups under Rear Admiral Clifton Sprague that comprised the only American forces remaining in the area. Composed of only six small escort carriers, three destroyers, and four destroyer escorts, Taffy 3 was intended to provide shore support and anti-submarine patrols, and did not have guns capable of penetrating the Japanese armor. The Japanese opened fire shortly after dawn, targeting Taffy 3's escort carriers, which Kurita mistook for the main carriers of the Third Fleet. The escort carriers fled for the cover of rain squalls and launched their aircraft in defense, while the three destroyers and destroyer escort USS Samuel B. Roberts, led by USS Johnston, launched a torpedo attack that sank one ship and sent the Japanese strike force into disarray.

A carrier battle group (CVBG) is a naval fleet consisting of an aircraft carrier capital ship and its large number of escorts, together defining the group. The CV in CVBG is the United States Navy hull classification code for an aircraft carrier.

The first naval task forces built around carriers appeared just prior to and during World War II. The Imperial Japanese Navy (IJN) was the first to assemble many carriers into a single task force, known as the Kido Butai. This task force was used with devastating effect in the Japanese attack on Pearl Harbor. The Kido Butai operated as the IJN's main carrier battle group until four of its carriers were sunk at the Battle of Midway. In contrast, the United States Navy deployed its large carriers in separate formations, with each carrier assigned its own cruiser and destroyer escorts. These single-carrier formations would often be paired or grouped together for certain assignments, most notably the Battle of the Coral Sea and Midway. By 1943, however, large numbers of fleet and light carriers became available, which required larger formations of three or four carriers. These groups eventually formed the Fast Carrier Task Force, which became the primary battle unit of the U.S. Third and Fifth Fleets.

The Battle of Leyte Gulf 23–26 October 1944, was the largest naval battle of World War II and by some criteria the largest naval battle in history, with over 200,000 naval personnel involved.

By late 1944, the Japanese fleet had become much weaker than that of the Allied forces; it contained fewer capital ships (aircraft carriers and battleships) than the Allies had aircraft carriers in the Pacific. After the catastrophic Battle of the Philippine Sea in June 1944, senior Japanese military leaders understood that their remaining naval forces were incapable of achieving a strategic victory against the Allies. However, the Japanese general staff believed that continuing to contest Allied offensives at sea was necessary to deter an invasion of mainland Japan and to give the Japanese navy an opportunity to use its remaining strength. As a result, the Imperial Japanese Navy (IJN) mobilized nearly all of its remaining major naval vessels in an attempt to repel the Allied invasion of the Philippines, but it was defeated by the U.S. Navy's Third and Seventh Fleets.

The Battle of Leyte Gulf, generally considered to be the largest naval combat in history, was fought 24–25 October 1944 in the waters of the Philippine Islands by elements of the Imperial Japanese Navy's Combined Fleet (bringing together the IJN's 2nd Fleet, 3rd Fleet and 5th Fleet) and the United States Navy's Pacific Fleet (bringing together the USN's 3rd Fleet and 7th Fleet). Of the five separate engagements that made up the battle as a whole, the forces involved in the three principal ones are listed here.

Since the Japanese assumed the tactical initiative in all three actions, their forces are listed first in each section.