Modern Japanese Swords and Swordsmiths by Hiroko Kapp, Leon Kapp, Yoshindo Yoshihara (2002)

Good informative book. Although it tends more toward Shin Saku To, there is some good information regarding Showa war time production (both mass produced and traditionally made blades)that I haven't seen elsewhere. Since these are the majority of swords that we encounter here in this country, the more information and learning a person can do on the subject it can only help.
Overall a worthwhile addition to your Japanese Sword Reference collection of books.