Between fine-tuning the final details on Tractics, Mike Reese occasionally explains rule rationale and gives me links to consider. For example, this one compares US and German artillery. The examples and anecdotes included add to my depth of knowledge and frequently gives me scenario ideas for future games.
This particular link also refers to a great book that would be worth looking for at the library. I owned a copy and got lots of good ideas from Closing With The Enemy: How GIs Fought the War in Europe 1944-1945 by Michael Doubler.
Another worthwhile reference are the US Army's “Green Books” of photos. The combination of the photos and detailed descriptions can spark an exciting game scenario. There are three books in the series and cover Northern Europe, North Africa/Italy and Japan. They can be downloaded for free as big PDF editions for free from the US Army's historical division. However, for today Chrome blocks to download due to some configuration problem.