John Boorman's 2014 follow-up to his well regarded "Hope and Glory" (which I haven't seen).
A comment I saw somewhere referred to this as the British Catch-22, and that's very accurate (although released 60 years later than the original, it's set in the same time period). In 1950, Bill Rohan (Callum Turner) is called up to army duty. There he meets Percy (Caleb Landry Jones), a man of considerably less morals than Bill who becomes his friend. Instead of being sent to Korea as they expect, they end up remaining at the training camp and teaching new recruits to type. The movie follows their (mis)adventures with girls, Bill's family, and their difficult superiors. The dark turn at the end isn't nearly so dark as Catch-22.