David Rae served in the British Army for 22 years. He retired as a warrant officer and regimental sergeant major—but not before completing four tours in Bosnia, one in Iraq and three in Afghanistan.

His specialty was armored reconnaissance. Now, he works on movies. Director David Ayer’s tank epic Fury was his first.

The film, out now, follows an American Sherman tank crew in the waning days of World War II. It’s 1945 and the Allies are on German soil, inching toward Berlin. Brad Pitt plays Sgt. Don Collier, commanding a Sherman named Fury.

Collier follows order, kills Nazis and struggles to keep his crew together after years of unrelenting warfare. It’s high drama—and Rae was on location to make sure it all looked right.

“Whenever the tanks were on set, I always stood to the right of the director,” Rae told War Is Boring. “I’d put a word in his ear if I ever thought something needed to change.”

Director Ayer went to great lengths to get World War II right. The production team sewed more than 700 military uniforms, then ripped out their buttons, blew out the pockets and covered them in mud to look like they’d endured long, bloody campaigns.

Ayer and his team located real wartime tanks. They tracked down World War II tank veterans for advice. But as cameras rolled, Rae was the final arbiter of the movie’s authenticity.

Rae on set with some of Fury’s cast. Sony Pictures photo

The job required compromise. “You can’t be 100-percent tactics-correct in a film,” Rae said. “It doesn’t allow for that, because of distance between vehicles or because a turret’s position cuts off an actor’s face. There’s a lot of practical concerns.”

Raid said the movie’s inaccuracies are minor—stuff that only someone who is already an expert in tank warfare will even notice. “The tactics employed in the film are pretty spot on,” he said. “The director has really done his homework.”

Ayer even cast the world’s last functional German Tiger tank.

The Tiger is an impressive machine. It’s heavily armored and packs a powerful 88-millimeter cannon. One Tiger could lay waste to several American Sherman tanks—and frequently did.

“It had an aura around it,” Rae said of Fury’s Tiger. “I had the honor of commanding it in the film. When you see a German pop out of the top, that’s yours truly.”

British troops captured the Tiger in North Africa in 1943. It destroyed two British tanks before its crew abandoned it. The Tiger now resides in the Bovington Tank Museum in England. Its appearance in this film is a big deal.

“It comes out once a year to make a lap,” Rae said. For Fury, the tank worked overtime—and never quit. “It never broke down. It never had a problem. It was in pristine condition inside and out.”

Wartime German tanks were pricey, complex marvels of engineering. By contrast, the Shermans were cheap, low-tech. The Germans favored quality. The Americans wanted quantity. And the only way a Sherman could defeat a Tiger was to outnumber it.

It was a costly tactic for the Allies. “Shermans were taken out by the boatload,” Rae said.