When does Strike Back return?

Strike Back is a British action thriller television series based on the 2007 novel of the same name by novelist and former Special Air Service soldier Chris Ryan. The series follows the actions of Section 20, a secretive branch of the British Secret Intelligence Service. The six-part first series began broadcasting on Sky One on 5 May 2010. The first episode of the ten-part second series, under the banner title Project Dawn, first aired on 12 August 2011. A ten-episode, fifth series titled Strike Back: Legacy aired in 2015, and at that point, this was to be final series for the show.