Books can be attributed to "Unknown" when the author or editor (as applicable) is not known and cannot be discovered. If at all possible, list at least one actual author or editor for a book instead of using "Unknown".
Books whose authorship is purposefully withheld should be attributed instead to Anonymous.
This is a collection of short essays on the historiography and many aspects of Russo-Japanese War. The essays are a lot of fun to read. It also gives an annotated bibliography.