I first read the book, when I was a young teenager, then saw the film late one night. About a year ago I checked it out on IMDb and discovered no copies available. I then hit the web and found a site that offers War Films, soooo glad that I did, ordered a copy and sat back and was able to confirm why I wanted to see it again.
In my opinion to really enjoy the film I suggest you read get a copy of the book and then watch the film. The book is no longer in print but I did track a copy down via E-bay, the Author Alan White was a commando/paratrooper during the 2nd world war taking part in disparate clandestine operations and this was his first book. It is written by someone who knows and this fact I believe gives the book and film authenticity. I have not given the film a ten only because of the nature of the ending of the film, not as good as the book. There are a couple of plot lines that differ from the book also, which is strange as the book is not about the large scale nature of war but about the individual in war. The film illustrates this exceptionally well. I have the copy of the book to let my son read and then the film to let him watch, in that order.
If you can track it down the book and the film then it is definitely worth it and I only wish that it was more readily available for more to read and see, one of my all best war films, ever!