A few months ago, we learned Christopher Nolan's next movie will be out in the summer of 2017. But we weren't let in on what that movie actually is. Now the mystery may have been solved, as reports from France, now confirmed by Variety, suggest some loose details on what could be the filmmaker's first war movie and his first period piece since 2006's The Prestige.

Here's what we sort of know of the project, which is currently titled Dunkirk:

A cast is already coming together

According to the Variety report, Mark Rylance, Kenneth Branagh and Tom Hardy are in talks to join the cast. None of their potential roles are known, unfortunately, but the trade refers to it as an ensemble cast, so expect even more names in the future. There will definitely be some teen roles, as Nolan's casting department is already scouting teen actors in London.

The movie will be based on a true story from World War II

According to the French site La Voix du Nord, Christopher Nolan and his screenwriting partner brother, Jonathan Nolan, have been scouting locations in Dunkirk, France, and researching the northern coastal town's significance during the Second World War. There's speculation that the movie will be about the Battle of Dunkirk and events known as Operation Dynamo. 

Operation Dynamo was a major evacuation of troops in 1940

Also known as the Miracle of Dunkirk, Operation Dynamo was a mission of the British government to evacuate more than 300,000 Allied soldiers, including French and Belgian troops and the British Expeditionary Force, who'd been trapped in the region by the Nazis during the Battle of France in 1940. Whether this mission will be the sole focus of Nolan's movie is uncertain.

The mission has already been the focus of a few movies

If Nolan's movie is specifically about Operation Dynamo, it won't be the first. There was the British film Dunkirk in 1958, featuring John Mills and Richard Attenborough, and the French production Weekend at Dunkirk, starring Jean-Paul Belmondo, in 1964. Much more recently, the evacuation was also part of the plot of Joe Wright's Atonement.

Nolan's movie will be at least partly shot for 70 mm

As pointed out by /Film, Quentin Tarantino recently let it slip that he knows Nolan will be working with 70 mm for his next feature. This isn't a big shock since he shot parts of his last four movies in the larger format, mainly for IMAX showings. But the idea is that this new one will also be made available for the 100 screens outfitted for Tarantino's The Hateful Eight 70 mm road show. 

The movie will shoot next spring and summer

At least the parts filming on location in Dunkirk will be shot in May and June 2016, according to La Voix du Nord, and reports of hotel booking in the area. Christopher Nolan's movie is due in theaters from Warner Bros. on July 21, 2017.