Five months ago we had the privilege of seeing Christopher Nolan’s “Dunkirk,” a magnificent work about the daring evacuation of the British Armed Forces that seemed to be hopelessly trapped by the Germans in the spring of 1940.

“Dunkirk” told the story from three points of view, which were essentially land, sea and air.

Although not officially affiliated with “Dunkirk,” Joe Wright’s “Darkest Hour” serves — and serves very well — as a prequel, told from a fourth point of view.

That of Winston Churchill.

Most of “Darkest Hour” takes place in the days and weeks just prior to the events of Dunkirk and focuses on the prime minister’s desperate efforts to formulate a plan to save those British troops, even as his opponents are saying Hitler has already won and it would be expedient to enter into peace talks with Mussolini’s Italy.

First, though, we meet Churchill just before he is to replace Neville Chamberlain as PM.

It’s morning in the Churchill household — a spacious and rambling and ever-so-slightly weathered townhouse bustling with activity. As Churchill rumbles and grumbles awake, like a giant bear shaking off a deep slumber, it’s as if a piece of vintage newsreel footage has started rolling.

We know this is Gary Oldman beneath the Oscar-level makeup and the padding. And yet within the first minute or so, we forget it’s Oldman and we marvel at one of the most authentic and memorable portrayals of Churchill in the long, the very long history of television series and movies about arguably England’s most important 20th century figure.

Oldman’s Churchill is a commanding presence as a public speaker and an occasional charmer when he wants to be — but he’s also a heavy smoker, an even heavier drinker, a short-tempered bully and someone almost incapable of the simplest of social graces.

Little wonder Lily James’ Elizabeth Layton, the latest in a revolving door of personal secretaries, is so intimidated she goes flying down the stairs within hours of starting the job. (Circumstances bring her back, and this time she stays.)

Little wonder many of Churchill’s enemies consider him reckless and dangerous and unfit to lead the country. Little wonder King George VI (Ben Mendelsohn) doesn’t even try to hide his disdain for Churchill each time they meet. The king winces at the man’s voracious appetite, his day drinking, his bluster and bravado.

The only one to stand up to Churchill on a regular basis, to calmly put him in his place even as she reminds him of his potential for greatness, is his wife Clementine (Kristin Scott Thomas in a finely nuanced performance). When the room is cleared and it’s just Winston and Clementine and the weight of the world on Winston’s shoulders, it’s Clementine who gives him the strength to take on the task.

Director Wright and his creative team do a masterful job of taking us into the underground bunker/war room where Churchill and his military advisers — and scores of support personnel — are holed up, collecting top secret intelligence and keeping on top of the ever-more-bleak war effort and mapping out strategies. From time to time we’re taken into the heart of the war itself, as when we see a regiment sent on a diversionary mission that is almost certain to result in their own deaths. Wright favors overhead shots that begin in close-up and rise up, up and up, painting a devastatingly effective picture of the sacrifice made by hundreds so that hundreds of thousands might live.

The more intimate set pieces are just as visually arresting, whether Churchill is meeting with the king at Buckingham Palace, in a cubbyhole and on the phone with FDR, or riding the train with an astonished group of citizens, asking their opinions on what he should do. (Although that latter scene represents the one time in the movie we go from sentimental and inspirational to hokey.) “The Darkest Hour” is filled with authentic touches, large and small.

Most authentic of all is Oldman’s performance as a flawed but deeply passionate man who summoned all of his courage, all of his oratory skills and all of his love for Britain at just the right moment, because the very thought of even one red Nazi banner hanging from a building in London was something he could not, would not tolerate.

Oldman can go as big as any actor on the planet, and he certainly plays to the rafters at times — but so did Winston Churchill. There’s a great physicality to the performance. Sometimes Churchill is so tired and defeated he can barely ascend a staircase; on other occasions he’s so filled with fire he practically runs through the streets, and his aides struggle to keep up with him.

As played by Oldman, Churchill has perhaps never seemed greater.

Or more human.

★★★1⁄2

Focus Features presents a film directed by Joe Wright and written by Anthony McCarten. Rated PG-13 (for some thematic material). Running time: 125 minutes. Opens Friday at local theaters.