These files are arranged chronologically. In the case of multiple documents in one file, the earliest date is used.
The collection has grown to the point that having all the files on one page is too awkward for easy use, so we've moved the periods to their own pages.
Some files, such as the Color Books, are in more than one period because they span multiple years.
Link to the University of San Diego's Time Line of WW2
These timelines should help you find the documents you're looking for, or you can email the Webmaster for help.
We have added (or will soon add) several hunred new files. (Beginning 1/30/2010.)