According to the conventional narrative, the U.S. military, barely surviving on half-rations, dozed through the interwar period until rudely awakened by the successive shocks of September 1939 and December 1941. Here Mahnken tells a considerably different story. Reassessing the performance of the U.S. Army's Military Intelligence Division and the Navy's Office of Naval Intelligence, he finds that those two largely neglected institutions performed with considerable effectiveness in the interwar period. Well before World War II, a cadre of American military attaches in Tokyo, Berlin, London, and other capitals had identified many (although by no means all) of the innovations that would prove decisive when war came. Mahnken also explores why authorities in Washington -- skeptical of evidence that departed from their own conception of warfare -- failed in too many instances to give that intelligence the credence it deserved. An important argument rendered with deftness and economy and rich in insights for those contemplating more recent failures of intelligence.