Strike Back: Shadow Warfare is the title of the fourth series in the Strike Back family of shows.
Series 1: (Chris Ryan's Strike Back) featured an ex SAS sergeant named John Porter who is recruited by a secretive arm of the military known as Section 20.
Series 2: ( Strike Back: Project Dawn) still featured Section 20 but had an almost completely new cast led by Amanda Mealing (Holby City), Sullivan Stapleton and Philip Winchester (Camelot).
Series 3: ( Strike Back: Vengeance) continues on from Series 2, but with minor cast changes, including the addition of Rhona Mitra (Underworld: Rise of the Lycans) as Maj Rachel Dalton.
Series 4: (Strike Back: Shadow Warfare), has the same main cast as series 3, but adds Robson Green (Wire in the Blood) as a new member of Section 20, Dougray Scott (Desperate Housewives) as rogue operative James Leatherby and Milauna Jackson (Blood Done Sign My Name) as a key player who crosses paths with the counterterrorism team.
Series 5 is currently in production (sept 2014).
Series 1 was produced for Sky TV, but from Series 2 the show was co-produced by Sky and Cinemax, resulting in slightly differing titles between the UK and US (UK series 2,3 and 4 lose their subtitles and become seasons 1,2 and 3 in the US).
Series 1 was shown in the US on Cinemax from October 2013 under the title Strike Back: Origins.