John S. McCain Jr., American admiral (d. 1981)
John Sidney "Jack" McCain Jr. (January 17, 1911 – March 22, 1981) was a United States Navy admiral who served in conflicts from the 1940s through the 1970s, including as the Commander, United States Pacific Command.

The son of a naval officer, McCain grew up in Washington, D.C., and graduated from the U.S. Naval Academy in 1931, after which he entered the submarine service. During World War II he commanded submarines in several theaters of operation and was responsible for sinking several Japanese ships, eventually being decorated with both the Silver Star and Bronze Star. After the war, he held a variety of commands, specializing in amphibious warfare. He led the 1965 U.S. invasion of the Dominican Republic. He also served in several posts in Washington, including the Legislative Affairs Office and as Chief of Naval Information, where he became influential in political affairs. He was a staunch anti-Communist, and his advocacy of a strong naval presence earned him the nickname of "Mr. Seapower".

During the Vietnam War, McCain was Commander-in-Chief, Pacific Command (CINCPAC), commanding all U.S. forces in the Vietnam theater from 1968 to 1972. He was a stalwart supporter of President Richard Nixon's policy of Vietnamization. McCain played a significant role in the militarization of U.S. policy towards Cambodia, helping to convince Nixon to launch the 1970 Cambodian Incursion and establishing a personal relationship with Cambodian leader Lon Nol. McCain was also a proponent of the 1971 incursion into Laos. He retired from the Navy in 1972.

His father, John S. McCain Sr., was also an admiral in the Navy and was a naval aviator; the two were the first father-son duo to achieve four-star rank. His son, John S. McCain III, was a former naval aviator who was a prisoner of war in North Vietnam during McCain's time as CINCPAC, who retired with the rank of captain and later became a United States Senator and the 2008 Republican Party nominee for President of the United States.