If you think you learned as much in History 101 as you'd care or need to know about the sinking of the Lusitania, think again. What you learned really wasn't all that much: that the ship was the pride of the Cunard Line, that she was sunk by a German U-boat in May of 1915 with the loss of 1,195 lives while en route from New York to England, and that the sinking hastened the United States along the road to active participation in the First World War. But to know that, as David Butler's terrific novel amply demonstrates, is to know almost nothing at all.

Yes, just when you thought they'd forgotten how to write intelligent, illuminating and entertaining historical novels, along comes "Lusitania" to prove that there's life in the old genre yet. There's so much life, in fact, that it fills nearly 600 pages to overflowing and leaves the reader happily exhausted as the novel reaches its sad, bitter conclusion. "Lusitania" is the real McCoy: an expansive, panoramic novel of the sort people used to have in mind when they said they'd like to curl up with a good book.

Butler has chosen, imaginatively and wisely, to tell the story of the Lusitania primarily through two men: William Thomas Turner, captain of the great liner, and Walther Schweiger, captain of the U-boat dispatched to torpedo her. Each in his own way is a company man, tough and ambitious but respectful of lines of command and determined to uphold the standards of the service in whose ranks he labors. Yet each also has more complex and appealing human qualities: areas of vulnerability and vanity, sensitivity and tenderness. The novel would almost certainly fail had either character emerged as sketchy or caricatured; that it succeeds is in substantial measure due to the subtlety with which both are portrayed.

The ship herself is, as she should be, a major character: "With her boiler rooms, engines and controls out of view below the waterline, to the world she was a floating palace, a vast, sumptuously decorated luxury hotel with accommodation for more than two thousand passengers and a crew of nine hundred. Nothing like her had ever been seen before." To one of the more notable passengers aboard for her final voyage, Alfred Gwynne Vanderbilt, she was a place for love: "A liner was an ideal place for romance, a self-enclosed, timeless world suspended between two realities, where all normal ties and obligations seemed less binding." But romance, need it be said, was not on the Lusitania's itinerary that May.

Which is what every reader of the novel knows, yet this in no way diminishes the suspense of Butler's careful, elaborate plot. Since the fate of the ship is a foregone conclusion, he turns our attention instead to other matters: How will Schweiger sink the ship and how will he feel about sending thousands of innocent, unwitting persons to a terrible death? What will be the reaction to this of the women with whom he has fallen in love? Which passengers will drown, which will survive? How will the rescue operations proceed?

These are the questions that the survey courses never got around to in the five minutes they devoted to the Lusitania, yet surely they are of as much interest and perhaps even importance as the matters of high diplomacy set off by the sinking. Though Butler hardly scants the larger issues attendant to the Lusitania affair, his emphasis is on the ordinary men and women whose lives were permanently altered by her unfinished journey. Kaiser Wilhelm ranting and scheming in his palace may attract our attention, but the fates of the Canadian couple and their children or the newlyweds from America attract our sympathy and concern. Without this human element, historical fiction has no real point.

Say it for Butler, though, that he is every bit as good on the big issues as on the ordinary people. His description of the workings of the U-boats is comprehensive and unfailingly interesting; the same goes for his explanation for the intense anger stirred within Germany against "neutral" ships and, more specifically, for the Kaiser's equally intense resentment of the Lusitania. "Lusitania" may not be a work of history, but there is enough sound history in it to satisfy all but the specialist.

It's also a book without any discernible pretensions. It is not literature and evidently does not aspire to be; Butler is not above melodrama and foreshadowing, and betrays no embarrassment at employing such familiar devices. There is no reason why he should. "Lusitania" is entertaining, informative and thoroughly engrossing--"popular" fiction of the very best kind. CAPTION: Picture 1, The Lusitania before 1915, a floating palace that became a war cry, UPI; Picture 2, David Butler; Copyright (c) Zoe Dominic