While Demi Moore and the rest of the main cast endured a mini-boot camp in Florida, Viggo Mortensen prepared for the role on his own for several months. He observed the actual training in Naval Base Coronado and talked to many active and retired Navy S.E.A.L.s. Some of the other cast members, with the exception of Moore, were angry that Mortensen didn't go through what the others had to go through. That's what Mortensen wanted.
In real life, Navy S.E.A.L. training (BUD/S) is conducted in Coronado, California. After graduating BUD/S, trainees complete Airborne training, cold weather training in Kodiak, Alaska, and the S.E.A.L. SQTs before being deployed. It can take up to two years before a S.E.A.L. sees combat.
Primary filmed on Camp Blanding (Florida National Guard) training base, near Jacksonville.
The Navy S.E.A.L.s opened up training to women in March 2016.