Pope's best naval yarn, again about the Yorke family (Buccaneer, and the densely detailed Ramage series), but updated 200 years to WW II. This one can only be called a meditative adventure tale, although the long thoughts are about ships, codes and cyphers, not mortality, and show Pope in smashing good humor. At 10 Downing Street, Prime Minister Churchill and Captain Watts of the Anti-Submarine Intelligence Unit explain to Lt. Commander Edward Yorke that the triumph he must bring off if Britain is to survive the war will call for ""diabolical cunning."" His security now cleared for A-1 Top Secret, Yorke is informed that Britain has possessed Enigma, the German cypher encryption machine, for two years and long ago broke its code. A year ago Germany switched to a new cypher, Triton, but now--horror of horrors--they've added two new cypher bails to their machine, plus a new cypher book, making the new Enigma unbreakable. Britain's greatest secret advantage will be lost unless Yorke can devise a plan for securing the new machine intact, with its new manual, without letting the Germans know Britain has a clear channel to the flow of German secrets. What Yorke eventually comes up with is a forlorn lifeboat set adrift in the North Sea with 20 commandos armed to the teeth. They are bait for any passing U-boat. After nearly two weeks in the open sea, when a German sub finally rises to sniff at the lifeboat, the commandos overwhelm the sub captain, stun his crew with harmless but superloud grenades and take over the ship. But getting a German sub, whose transmitter is burned out, safely into British waters, makes for intense storytelling. Wartime London, as well, is richly nostalgic.