John Wayne never served a day in the military, but he certainly was one very vocal supporter of the troops.
During World War II he tried to enter the military, but between a series of old injuries from his acting career and a bodysurfing incident, his family situation, and the maneuverings of a studio head, his efforts were thwarted, according to the Museum of Military Memorabilia.
John Wayne in Operation Pacific, a 1951 film centering on the submarine service during World War II. (Youtube Screenshot)
Wayne did make USO tours in the South Pacific in 1943 and 1944, well after the fighting there had ended. But he made a number of iconic World War II films, including "They Were Expendable" in 1945, "The Sands of Iwo Jima" in 1949 (where he was nominated for an Oscar), "The Longest Day" in 1960, and "The Green Berets" in 1968. In "They Were Expendable," the producers of the film worked with Medal of Honor recipient John Bulkeley.
One film that doesn't get the attention of these other classics is "Operation Pacific," released in 1951, which featured retired Adm. Charles Lockwood, the former commander of the Pacific Fleet's submarines during World War II. Wayne played the executive officer, then the commanding officer, of the fictional submarine USS Thunderfish in this film.
VADM Charles A. Lockwood, who served as technical advisor for Operation Pacific. (US Navy photo)
Given Lockwood's involvement, it's no surprise that the film features some of the notable submarine exploits of World War II, compressed into one story — including Howard C. Gilmore's famous "Take her down" orders, and the effort to fix the badly flawed torpedoes that dogged the U.S. Navy's submarines for the first portion of the war.
The film's climax featured an incident that composited the attacks on Japanese carriers during the Battle of the Philippine Sea with the actions of the submarines USS Darter (SS 227) and USS Dace (SS 247). The film is notable for showing the many missions the subs of World War II carried out, from evacuating civilians to rescuing pilots to, of course, sinking enemy ships (the Thunderfish's on-screen kill total included a carrier, destroyer, a Q-ship, and a submarine).
You can see the trailer below. The film is available for sale on Youtube.