The film, by Finnish director Timo Vuorensola, is set in 2018. The Nazis moved to the moon after their defeat at the end of the second world war. They build a community, and military forces, ready to take their revenge.
Shot mainly in Frankfurt, Germany, and Australia's Gold Coast, the Finnish-German-Australian co-production premiered at Germany's 62nd Berlin International Film Festival in February last year.
"It's a real conspiracy theory," says Jarmo Puskala, the film's community manager, who came up with the concept. "By that, I'm not saying it's real, but people actually believe that the Nazis went to the moon. I thought it was a hilarious idea."
Some of the film crew have known each other for a long time, and worked on Star Wreck, a series of popular Finnish Star Trek parody movies. They discussed the idea of Iron Sky one evening, and soon "agreed make a movie about moon Nazis", Puskala says.
But making a comedy film about the Nazis is always going to be controversial.
The Nazi leader Adolf Hitler, who ruled Germany from 1933 to 1945, started the second world war by invading Poland. They went on to murder millions of Jewish people.
One of the challenges for Vuorensola was how to tackle this difficult issue.
"There weren't that many films out there for reference," he says. "We often asked ourselves, 'Is this OK? Do we know what we're doing?'"
After a lot of research, the team realised making fun of Nazi ideas was fine, but they would steer clear of the victims.
The mocking starts early in the film. One scene shows a classroom of moon-dwelling children. The only thing they have been taught is elitist Nazi ideology, and they believe they must return to save Earth's helpless people. Hilarious, if you think about what the Nazis did.
The movie features epic graphics and visual effects, created by led by Finnish artist Samuli Torssonen's CGI team.
The film faced many stumbling blocks when it came to being distributed. Producer Tero Kaukomaa says they initially pitched the idea to German distributors.
"At the start it was very promising," he says. "But, a little later, when we started to talk about the distribution deal in detail," he says there were a lot of questions.
A lot of people were nervous about how to market a comedy about such a sensitive subject. Luckily, Iron Sky received a warm reception in Germany when it was screened.
The filmmakers' "secret weapon" has been its massive online fan base. The Iron Sky film team are in contact with about 250,000 people each week. Many have been fans since the Star Wreck series and, through "crowdsourcing", contributed ideas and funds.
Fans provided 10 per cent of the whole Iron Sky production budget, while their support gave Vuorensola and his team greater bargaining power when asking for additional funding.
The production crew, now in France at the annual Cannes Film Festival, are working on Jeremiah Harm, a film of the American graphic novel about a galactic bounty hunter.
Vuorensola says they will also film a sequel to Iron Sky, and will reveal details at this week's film festival. "There'll be lots of 'crowdsourced' funding for that film," he tells Young Post. "Hopefully, it'll be even bigger than Iron Sky."