When does Strike Back return?

Strike Back is a British/American action-adventure/spy-drama 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 (SIS, aka MI6) 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, with the last episode airing on 29 July.