Most people know about the German Enigma cipher, and how the British at Bletchley Park successfully cracked it, greatly aiding in winning the war ...
Very few know about the Japanese Naval (JN25) and Diplomatic (”Purple”) ciphers and how the American Navy and Army codebreakers successfully cracked it, greatly aiding in winning the war ...
Magic: The Untold Story of U.S. Intelligence and the Evacuation of Japanese Residents from the West Coast During Ww II
https://www.amazon.com/dp/0960273611
Great book. We knew a lot, and acting on it wasn’t easy.