From that site:
This is not a remake of the 1941 Crown film service documentary of the same name, but a story of a bomber crews mission to Berlin in 1944. Although fictional it could have been the true story of any of the thousands of sorties carried out by bomber command during the second world war. Filmed entirely on location at a former RAF station in Lincolnshire, it follows S/L Les Andersons crew from briefing to raid and then the tough journey home.