The image I'm using on the cover is a close up of a portion of a tank. While choosing this, I consciously made use of the “Pars Pro Toto” style figure. ("Pars Pro Toto" means "Part of the whole.")
Because you only show a part of the tank, fanatics are already thinking about which tank it is, or maybe they'll recognize it right away. If they recognize it right away, they will probably feel some pride because they know it and others, probably, don't. In this way the cover will make them feel good and they'll be more likely to buy or read it. Throughout the entire recognizing- and knowing process you appeal to the audience you're targeting more and you encourage them to do something when they see the book
The choice in font is something I decided because it resembles the real stencil and army fonts a lot. I also think it fits really well because of how present and in your face it is, just like tanks are.
And last but not least; I used the color orange a lot. I chose to do this because it's the national color of The Netherlands, and in war nationalism always plays a huge part so since this book is published and written by a Dutch company and the main subject is war, I decided to use it.