Here is a list of books that are helpful when dealing with military cups. I am
not going to include every good book about the Japanese military; that list
would be too long. I just want to give sake cup collectors an idea of what
books can help them enjoy the hobby more.
A Dictionary of Military Terms,
English-Japanese, Japanese-English
by Lieutenant Colonel H.T. Creswell, Major Hiraoka, Major R. Namba
The University of Chicago Press 1942 (I have the seventh impression, dated 1946.)

An excellent bi-lingual dictionary that is restricted to military terms. Absolutely
wonderful! It has answered a lot of my questions about kanji and translations. Long out
of print, but you can find one at online used bookstores for about $40.
The Elements of Japanese Design,
A Handbook of Family Crests, Heraldry, & Symbolism
by John  Dower, 1971 (I have the fourth printing, dated 2005.) Still in print.

Since many cups have kamon (family crests) and other crests, this book helps a lot in identifying and
explaining them. Although most crests were non-military, a number of crest images (such as the
gourd) appear on military cups.

Another good Japanese crest book:
Family Crests of Japan
No author listed.  ICG Muse, Inc., 2001 Still in print?
Concise Dictionary of Modern Japanese History
Compiled by Janet E. Hunter 1984  I don't know if it is still in print.

Short entries that not only identify the political and military figures since the Meiji period, but also
various battles, conflicts, and treaties. The kanji for the names and battles are also included, which
helps a lot when trying to figure out exactly which conflict is being referred to on the cups.
Japanese Army Handbook, 1939-1945
by George Forty 1999 (Mine is dated 2002.) Still in print.

Superb explanations of the organization of the IJA. All relevant
vehicles explained, which helps in identifying vehicles on cups. Also
details many aspects of different units.
Orders and Medals of Japan
and Associated States
by James W. Peterson (I have the third edition, dated 2000.)

The best (only?) book on official medals and badges from Japan. You can see a
variety of badges on sake cups, and once in a while you'll see a medal, too, for
example, the Golden Kite medal. Anyway, this book is fantastic (though due for a
fourth edition). What is missing is the Japanese names of the medals (in both
kanji and romaji).
HEITAI-HAI (Soldier's Cups)
by Mutsuki Kato (first edition, dated 1984)

The first  book on Japanese military sake cups. The text is in Japanese. Kato divides
the cups in different groups (cavalry, transport, artillery, engineer, etc.) and shows
the different themes and designs used by those groups. The first group of cups are
more important historically than aesthetically; Kato does not hesitate to include
chipped or faded cups. He is more interested in what they signify.
Japanese Military Sake Cups 1894-1945
by Dan King (first edition, dated 2004)

Full of interesting photos and some good background. A number of the
pictures are not directly related to cups since Dan appears to be trying to put
them in a larger historical perspective. Quite a few rare cups shown in this
book, but the values listed are dated.
Japanese Military Sake Cups
by Richard Fuller (only one edition of this book, reported to be only 100 copies.
Published in 2002)

Here is an excellent beginning resource book for sake cup collectors. Though
it doesn't have many pictures, the text is quite informative, despite the fact
that Mr. Fuller didn't have access to a large number of examples.
Daruma Magazine
Although this magazine is dedicated to Japanese fine arts, a few of the issues
have military-related goods (such as #8 and #52). A short essay by Alistair
Seton on sake cups is in Daruma #4. Glossy pages, nice color photos.
Published 4 times a year.

Here is the home page where you can order back issues:
Military Sake Cups Bottle and Trays
by T.L.O. Militaria. Number 1 Winter 2001 Spring 2002

Not exactly a resource since it is a sales catalog. However, the pages are all
color and glossy. Full of interesting photos. Inside the author says there will be
a Catalog #2 as well, but I don't know if it was ever printed.