Book excerpt: Why was the Navy ready to clear the skies over the Persian Gulf, yet surprised by the mines laid under it? Why is it that the Army is always prepared for war in Europe, but was caught off guard in Korea and Vietname? And why is the Air Force indifferent to "Star Wars"? In The Masks of War Carl H. Builder asks what motives lie behind the puzzling and often contradictory behavior of America's militay forces. The answer, he finds, has little to do with what party controls the White House or who writes the budget. Far more powerful-and glacially resistant to change-are the entrenched institutions and distinct "personalities" of the three armed services themselves. The Masks of War explains why things sometimes go wrong for the American military. It also explains why things will always go wrong for the military reformers. Changes in the military's strategic thinking have come only in the wake of full-blown disaster-Pearl Harbor, for instance. Today's nuclear world can't afford such lessons.