Strike Back is a British/American action-adventure/spy-drama television series based on a novel of the same name by novelist and former Special Air Service (SAS) soldier Chris Ryan. The series follows the actions of Section 20, a secretive branch of the British Defence Intelligence service (DI), who operate several high risk, priority missions throughout the globe. The six-part first series began broadcasting on Sky One on 5 May 2010. After a second series was commissioned, it was announced that Cinemax would co-produce the franchise. The first episode of the ten-part second series, under the banner title Project Dawn in the United Kingdom, first aired on Cinemax on 12 August 2011. The ten-part third series, under the title Strike Back: Vengeance, began airing on Cinemax on 17 August 2012. On 3 October 2012, Cinemax and Sky commissioned a fourth series, Strike Back: Shadow Warfare, which was broadcast on Cinemax beginning 9 August 2013. A ten-episode, fifth series titled Strike Back: Legacy aired in 2015, with the last episode airing on 29 July, and at that point, this was to be final series for the show.