Actor John Wayne, left, speaks with Maj. Gen. Graves B. Erskine during the filming of “Sands of Iwo Jima” in 1949. (Marine Corps photo)

President Trump had a John Wayne moment Friday.

In his latest warning to North Korean leader Kim Jong Un, Trump declared the American military “locked and loaded,” and equipped with “solutions” if Kim’s increasingly isolated regime refuses to cease its nuclear provocations.

In doing so, the commander in chief evoked lingo popularized by the Duke but long used by U.S. troops in combat and those training for war.

The expression is used among many shooting enthusiasts, too. But it was Wayne, portraying Marine Sgt. John Stryker in the World War II film “Sands of Iwo Jima,” who introduced “lock and load” to the broader American lexicon in 1949.

The expression appears at least three times in the film: twice as the Marines gird for battle, and once when Wayne’s character is offered a drink of bourbon. “Lock and load, boy,” the Duke enthusiastically replies. “Lock and load.”

The White House did not respond to questions seeking insight into Trump’s decision to use the expression in his tweet Friday, and whether “lock and load” is something he says routinely.

Trump has long admired Wayne, however. He has used Twitter previously to share inspiring quotes from the Duke — “Courage is being scared to death, but saddling up anyway” — and to publicize an endorsement from the late actor’s daughter ahead of last year’s Republican primaries.

It’s tough to nail down precisely where the expression originated. Questions to that end come up frequently on firearms message boards.

The Oxford English Dictionary cites a news article, published by the New York Times in November 1940, that references a military range officer who “boomed through his microphone, ‘Lock and Load.’ ” Another forum suggests the expression could date to the late-1800s.

Often, such discussions point to an entry on the Saving Private Ryan Online Encyclopedia, a site created by fans of the 1998 World War II drama starring Tom Hanks. That site defines the term thus:

One explanation comes from the actions needed to prepare a flint lock rifle for firing. In order to safely load a rifle of this type it was necessary to position the firing mechanism in a locked position, after which the gun powder and ball could be safely loaded into the rifle barrel without any chance of the rifle misfiring.

The second explanation is that the phrase originated during World War II to describe the preparations required to fire an M1 Garand rifle. After an ammunition clip was loaded into the rifle the bolt automatically moved forward in order to lock a round into the chamber.

The Marine Corps Silent Drill platoon performs during an evening parade at Marine Barracks Washington on May 1, 2015. (Lance Cpl. Kayla V. McTaw)

The military no longer fields the M1 Garand to its operational units, though the rifle still appears at ceremonial events.

And while the expression remains relevant on military rifle ranges, “lock and load” is used less frequently on the battlefield. Rather, most combat units have a color-coded system to signify a weapon’s status. For rifles, green means it’s unloaded. Amber indicates a magazine is inserted. Red signals a round is inside the barrel.

Still, the expression remains deeply ingrained in the military’s vernacular, said Gen. Charles Krulak, who spent 36 years in the Marines and served as the service’s commandant before retiring in 1999. His wife even says it when responding affirmatively to some questions — as the Duke did when agreeing to join his buddy for a drink.

The president’s rhetoric is “not always helpful,” Krulak told The Washington Post, saying he does not believe it implies military action is imminent. Nevertheless, he added, no one should confuse what “locked and loaded” signifies.

“It’s been used by men, and now women, literally going into combat,” he said. “When they’re moving toward the sound of guns — and the smell of cordite.”

Mike Rosenwald and Alex Horton contributed to this report.

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