The French Indo-China War of 1946-54 was one of the longest and bloodiest conflicts of the twentieth century. The French had attempted to reinstate their colonial rule over the region after World War II, but by 1953 it was obvious that they were slowly losing the war to the Viet-Minh, supported by Communist China. In late 1953 the French High Command decided to occupy the valley of Dien Bien Phu in northwestern Vietnam.Dien Bien Phu became the site of the most decisive battle of the French Indo-China War. Indeed, the outcome at Dien Bien Phu set the stage for America's military involvement in Vietnam a decade later. Yet despite its importance, there is still uncertainty about why the French chose to make a stand at a place that, in hindsight, involved such risks.In The Undetected Enemy, John Nordell examines that question by telling the full story of the strategic, tactical, logistical, and intelligence considerations that underlay the French decision. This book also gives close attention to the reaction of the Eisenhower administration to the Dien Bien Phu operation, an important part of the story that, until now, has been overlooked. Historians have preferred to focus on the climactic siege of Dien Bien Phu in the spring of 1954, when the issue of U.S. intervention hung in the balance. The Undetected Enemy looks at the period preceding the battle for the valley, when U.S. officials, including the president, responded with optimism or, even worse, indifference to the French operations.Using war memoirs and archived documents only recently declassified, the author weaves a compelling narrative of rapidly unfolding developments during the buildup to the siege. For military enthusiasts and historians, this story, written from the perspective of the participants themselves, answers the decades-old question, "Pourquoi Dien Bien Phu?"