The thing about the great film stars of the past is that they’d often as not embrace their screen “persona” and rarely make the effort to “stretch” as an actor. Bette Davis to Tracy, Peck and Wayne to Deborah Kerr and Joan Fontaine, they might fight for chewier, showier awards-bait “better parts.” But by an large, they accepted a form of type casting.

Robert Mitchum, a man’s man, quintessential screen tough guy, a good-looking version of Bogart who played a lot of gumshoes, lawmen in the saddle and the occasional villain (like Bogie) didn’t stretch much. He didn’t need to. He could render archetypal characters layered, conflicted and fascinating to watch.

His over-the-top villainous turn in “Night of the Hunter” might have been his biggest stretch. But a close second might be a role that had him slinging a very convincing Irish accent, singing and throwing the occasional punch as an IRA man who tells his murderous comrades “I’m quittin’ the IRA.”

You know what that means. “Nobody QUITS the IRA!” And there isn’t much of a leap from that to “INFORMER!”

“The Night Fighters,” a 1960 Irish production, has hints of John Ford’s 1935 classic “The Informer,” an Irishman struggling with his conscience, trying to do the right thing and yet have something of a life beyond “the cause.”

“The hell with the cause,” isn’t what triggers Victor McLaglen’s Gypo Nolan to turn “Informer” on 1930s Irish Republicans in that Oscar winning film. Gypo’s trying to get his hooker/girlfriend off the streets and off to America for a fresh start. He does it for the money, and the guilt and fear of discovery tear him apart.

Mitchum’s Dermot O’Neill’s loyalties are deeper, more personal. His wounded comrade (Richard Harris), the fellow he carried to safety, singing old Irish folk duets along the way, is who he’s loyal to. His longtime lady love, the hairdresser Neeve (Anne Heywood), deserves better than an impoverished life in Northern Ireland, better than a 35 year-old beau who drinks and lazes about and joins the IRA pretty much on a dare. He’s loyal to her, too.

The “cause” and the IRA? Not so much.

It’s 1941, and the IRA has allied itself with Nazi Germany, which has trained and equipped operatives to lead a rebellion against Britain that might coincide with fading German hopes of invading the UK. Irish Republicans, desperate to “unite these counties” with the Irish Republic “at last,” make their deal with the devil and hope for the best.

More than a few recruits mutter about linking themselves to Nazis, but they take on a mission — blowing up a hydro power plant. That’s what gets Sean shot and gets Sean caught. And that’s all she wrote for the two fisted fighter, two-fisted “sharing a jar” (drinker) Dermot.

The increasingly fanatical local IRA commandant (Dan O’Herlihy, perfect) can’t dissaude Dermot from complaining about his mate Sean’s imprisonment, can’t inspire him with speeches about the “bigger than one man” cause.

That’s what devolves from a heated argument to mortal threats, with an IRA “trial” and execution in the works.

This isn’t the most satisfying tale of Ireland’s off-and-on-again “troubles.” But the film, also titled “The Conspirators” in some markets, and “A Terrible Beauty,” and based on a novel of that name, is as vividly Irish as “The Quiet Man,” but with grit and grim black and white reality instead of whimsy, folklore and Technicolor.

Harris, very early in his career, is in tip top form, with O’Herlihy impressive as always and Cyril Cusack playing a local sage who sees a better Ireland without violence excellent in support.

And Mitchum is a delight as a tippler slow to anger but handy with his fists, an impulsive younger brother to the even drunker Ned, played by the great Irish character actor Niall MacGinnis. Mitchum adds a light touch to his tough guy persona that he wears as easily as that Irish lilt.

Direct Tay Garnett, who got his start in the silent cinema, manages some splendid action beats on location in Ireland (County Wicklow, etc.) and delivers lovely screen compositions, even in day for night outdoors shots.

“The Night Fighters” is untidy like its many titles, ungainly, and melodramatic at the end. But any Mitchum completist looking for another title to throw out there in “most under-rated leading man EVER” arguments will find a lot to like and a little to love in this outing.

Mitchum leans into his “type,” but stretches, singing and laying on the brogue like Sean O’Casey himself as a man who wonders if the Irish Republican Army is getting himself and his people closer to their dreams of a united Ireland, or pushing those further into the future.

Rating: unrated, violence

Cast: Robert Mitchum, Richard Harris, Anne Heywood, Marianne Benet, Cyril Cusack and Dan O’Herlihy

Credits: Directed by Tay Garnett, scripted by R. Wright Campbell, based on a novel by Arthur Roth. A United Artists release on Tubi, Amazon, Youtube, etc.

Running time: 1″30