Philip Winchester, who plays Stonebridge, is an American actor playing a British character. Sullivan Stapleton, who plays Scott, is an Australian actor playing an American character.
All the English female actors along with their male counterparts had extensive training with British SAS and SBS instructors.
Before the second series, main cast members took up intensive bootcamp style training in South Africa by former SAS and SBS operators. Sullivan Stapleton and Philip Winchester underwent the most intensive training. The actors were trained in many aspects including running, teamwork, tactical manoeuvres with and without weapons and other various military tactics.
Before Damian Scott (Sullivan Stapleton) was created for the series, the writers briefly considered having the character of Felix Masuku (Shaun Parkes) become the main character in the show. The idea was scrapped after Richard Armitage decided not to commit to a new season.