Strike Back is a British/American action and military 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 series began broadcasting on Sky1 on 5 May 2010, showing the first six-part series. 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, which was broadcast on Cinemax beginning 9 August 2013. A ten episode fifth and final season aired in 2015. The final episode aired on 29 July 2015.