Storm of Steel: The Development of Armor Doctrine in Germany and the Soviet Union, 1919–1939

This is an incredibly-detailed account of the evolution of pre-war armored doctrine in Germany and the Soviet Union, and seems to cite every pamphlet, manual, or article written by every obscure author in both countries (and other countries!) during the pre-war period, with very extensive footnoting.  Given the topic, it is probably inevitable that this book makes for rather dense reading, but it is not helped by the book's academic writing style.  If you need to know about the evolution of pre-war armored doctrine, you need this book, but otherwise I suggest that the general reader give it a pass.