I found his Berlin Diary on sale and read it this spring. Very interesting reading, but it would help to know some of the players beforehand.
I'll have to find it. Another one he wrote is "The Collapse of the Third Republic" which tells the story from the French side. It is written ten years later (1970). Very interesting as to what was going on in France, which was considered to have by far the strongest army in Europe until about 1936 or 1937.