Biddiss, a former paratrooper, started his film career as an extra on the movie "Monuments Men."
Since then, he has worked on projects like "Mission: Impossible Rogue Nation," HBO's "Catherine the Great," and "The Crown."
"I always tell people military film advising is 60% research and 40% of my own military experience added in to the mix," Biddiss told Insider by email.
To prepare for a shoot, Biddiss obtains authentic training manuals appropriate to the conflict.
"I like to first understand the recruitment and training process, the rank structure and attitude between the ordinary ranks and officers," he said. "This helps me better understand the battles and tactics used by the men and what must have been going through their heads at the time."
That helps him structure a training program appropriate to the conflict, and safe for the performers — even when he's short on prep time.
"When tasked to train 500 supporting artists for [the BBC's] 'War and Peace,' I only had three days to research Napoleonic warfare and prepare a safe structured training program before flying out to Lithuania to train the men before a large battle sequence."