Ever since By the North Gate Gwyn Griffin established that he was an uncommonly able writer and at his best when he has not been trying to recruit a popular audience. Inadvertently he may. have done so here in as uncompromising a book as he has written, long, but still retaining the terse, graphic, incisive virtues of his talent, The first quarter of this book deals with the ""operational necessity"" of the title in which a German U-boat, under the command of its Kapitanleutnant Kielbasa, riddles and rams the derelicts on a raft of the freighter it has torpedoed. There is only one survivor, and the U-boat (this takes place at the close of the war) hopes to find sanctuary ih neutral territory, instead is brought in under English jurisdiction in Africa. The Captain, along with the young Emil Kummerol who carried out the orders who is hospitalized for months with a severe leg injury, survive the end of the war. Kielbasa and Emil (who had hoped to make a getaway) are brought to trial and almost half of the book here deals with their infraction of the' rules of warfare of International Law andtheir offense against the ""Law of Nations."" The sentence, and its execution, however, makes a much larger indictment and one is left with a sense of the gratuitous, outrageous inhumanity of any military action. The novel reads with authoritative tension and it is a cumulatively implacable, impressive performance.