Book excerpt: The Elusive Enemy explores the evolution of U.S. intelligence concerning the combat capabilities of the Imperial Japanese Navy and its air arm during the interwar period and the Pacific War. Ford contends that the US Navy could not accurately determine the fighting efficiency of Japan’s forces until it engaged them in actual battle conditions over an extended period. As the conflict progressed, the Americans were able to rely on a growing array of intelligence material, including POWs, captured documents, and specimens of captured enemy weapons. These sources often revealed valuable information on the characteristics of Japanese equipment, as well as some of the ideas and doctrines which governed how they carried out their operations. First-hand observations of the Japanese navy’s performance in battle were the most frequently used source of intelligence which enabled the US Navy to develop a more informed assessment of its opponent. Ship crews, along with US aviators, were tasked to collect information by making a thorough observation of how the Japanese fought. Action reports described how the Imperial fleet demonstrated a number of weaknesses, the most important of which was a shortage of modern equipment and, after 1942, diminished air power. Yet, he demonstrates how the Japanese remained a resilient enemy who could be defeated only when the Americans deployed sufficient equipment and used it in an appropriate manner. The Office of Naval Intelligence, as well as the intelligence services operating in the Pacific theater, thus had to assess a wide array of conflicting characteristics, and provide a balanced evaluation concerning the strengths and weaknesses of the Imperial navy. At the same time, a large part of the intelligence analysis was undertaken by commanders in the Pacific Fleet. Naval personnel and aircrews assessed the information gained through encounters with the enemy so that they could develop a set of methods whereby US forces were able defeat the Japanese without incurring excessive casualties and losses. The intelligence services, in turn, played an important role in disseminating the information on the most efficient tactics and weapons that could be used to defeat the Imperial Fleet. The Elusive Enemy aims to explain how American perceptions concerning the Japanese navy evolved during the conflict, with a particular focus on the role of intelligence. It also seeks to introduce a new perspective on the question as to why the U.S. Navy carried out its campaigns during the Pacific War in the manner that it did.