I had some very quick thoughts about the direction of my dissertation. Various different types of authors are beginning to emerge in my thinking. Some of the TM authors were clearly military engineers. The most obvious example is Ramelli. Errard and Bachot, however, may have gained more notoriety through their fortification designs. Lorini is also a noted TM author who is primarily known as a fortification engineer.
The sketch book may have been an important The sketchbook at the LOC certainly seems to point to this range of practices.
Another slew of authors had more civil aspirations. Bockler and de Caus explored gardens and automata in addition to hydraulic machinery. Joseph Furttenbach had even wider interests and included fortifications and cannon in his designs.
Heinrich Schickhardt presents another view on the machine books. As a civil engineer, he was concerned with both architecture and early industrial machinery. It's unclear if he also explored fortifications although his designs seem primarily civil/industrial rather than martial.
In all of this Besson is an enigma. What exactly was that dude up to? His background is anomalous.