Released in cinemas today, Lone Survivor tells the incredible true story of a unit of US Navy SEALS who found themselves surrounded by militia fighters in the mountains of Afghanistan.

A huge hit in the US, the film stars Mark Wahlberg, Taylor Kitsch, Emile Hirsch and Ben Foster, all of whom had to go through some serious training to make the film as realistic as possible. Here're five things you need to know about Lone Survivor: 

1. The film is based on the memoir of Marcus Lutterell, one of the Navy SEALs who was on this deadly mission. 

2. The siege lasts three days in the movie. In real life, it lasted five days. Think about that: a five day firefight. 

3. All the actors had to go on a three-week bootcamp where they worked with real SEALs and live ammunition. 

4. Lone Survivor won a SAG (Screen Actors Guild) award for its stunts. 

5. Director Peter Berg 'embedded' with an active SEAL team in Iraq for a month in order to help accurately portray them. Watch the trailer below.