Fisk researched the hell out of this subject and it it's all in this book. It's a prototype Fisk book, his thesis on Irish neutrality during WWII. At its best, he unearths an interesting story that he skillfully ties into the modern day (at the writing, a time when both Ireland and Germany were partitioned). At worst, he buries the reader in unnecessary details that grind the narrative to a halt. Fortunately, in his later books he doesn't do that.