This takes a while to get going, the handling is clearly flabby (it was John Sturges' last film as director and he was in decline), it's too long and some of the casting is irritating, but it's a cracking yarn from a terrific source novel - Jack Higgins' clever best seller - and steadily gets better as it goes along.
It took me a while to get used to Michael Caine playing a German officer, even if Caine does look teutonic, but once I did I enjoyed his performance. Conversely, I started off enjoying Donald Sutherland's IRA man for his humour and energy but eventually got sick of him - I never believed him as a man of action, great lover, or soulful philosopher (they badly needed Richard Harris, Richard Burton or Peter O'Toole - someone with sadness and gravitas rather than simple mischeviousness).
Robert Duvall is pretty good as the German mastermind of the operation and Jean Marsh (traitor), Donald Pleasance (a chilling Himmler) and Larry Hagman (idiotic American colonel) are superb in their roles. Solid support from Treat Williams (as a competent American officer - I wonder if part of the reason this didn't do that well in America was its depiction of a disastrous American raid). Anthony Quayle's nice German admiral was distracting. Jenny Agutter is the Sutherland's love interest and the ever perky Judy Geeson pops up.
It's hard to think of a film made by an Allied country set in World War Two that had more sympathetic German characters - Caine's character is sentenced to a penal battalion for helping a Jewish woman escape, Quayle is anti-Nazi as is Duvall, Caine's Germans like to play the organ in church, are super competent and loyal soldiers and are only exposed after helping save a girl from drowning. In contrast, the English village includes a traitor, a bully and some massively incompetent American soldiers.
There is some decent action towards the end. Tom Mankiewciz wrote the script; I'm never sure how good a writer he was - it was the source material, surely that made this good - but it seems to be from my vague memory of the novel a solid, faithful adaptation.