Bataan Diary By Capt. Paul Ashton (12th Medical Regiment, Philippine Scouts)
For so long I've resisted buying this book because it's been out of print and pretty expensive. I decided to take the plunge and buy it and for the history buff/researcher type, it's worth its price in gold. I paid $50 for this one. I let some cheaper ones go on ebay in the past (kicking myself). However it was a pleasant surprise to find out that this book was signed by the author! I've only read about 30 pages so far but it's the most detailed in terms of descriptions, daily life at Fort McKinley, army life, field exercises, detailed descriptions of prewar Manila, etc. I'm sure the rest of the book that deals with the war and postwar will not disappoint. It has lots of pictures and a huge appendix of official correspondences, typed orders, army records, etc. It's a huge voluminous book. I highly recommend it for the serious history buff of that era.
I just bought this one used from Amazon. I was surprised to see it signed by the author. I'll email you the raw picture of the cover so you can zoom in and examine the unit patches. I see that the 21st division patch on this one used Roman numerals.