The movie apparently didn't make a dent at the box office, and, to be fair, the movie probably does take some prior knowledge of the historical situation to make sense, but I think it's a good movie overall. Robert Mitchum's accent isn't even the worst, although the crazy variety of Irish accents alone (on the actual Irish actors) who are supposed to live in the same town and/or be related to each other is fairly entertaining! I think I heard exactly one actual northern accent in the whole thing... Ah well, such is Irish filmdom.
A young Richard Harris (this is his fifth movie in the first two years of his acting) is another bright spot in the film, for sure. Mitchum and Harris make a great pair of friends, and the great little twist of Harris' character being a Protestant among the IRA men is a perfect touch, historically speaking.
Unfortunately, the film is not available on You Tube (nary a trailer or anything). Amazon does have it.