Let's look at Mattis' successor:
https://dod.defense.gov/About/Biographies/Biography-View/Article/1252116/patrick-shanahan/
Patrick M. Shanahan became the 33rd Deputy Secretary of Defense on July 19, 2017.
Mr. Shanahan most recently served as Boeing senior vice president, Supply Chain & Operations. A Washington state native, Mr. Shanahan joined Boeing in 1986 and spent over three decades with the company. He previously worked as senior vice president of Commercial Airplane Programs, managing profit and loss for the 737, 747, 767, 777 and 787 programs and the operations at Boeing's principal manufacturing sites; as vice president and general manager of the 787 Dreamliner, leading the program during a critical development period; as vice president and general manager of Boeing Missile Defense Systems, overseeing the Ground-based Midcourse Defense system, Airborne Laser and Advanced Tactical Laser; and as vice president and general manager of Boeing Rotorcraft Systems, overseeing the Apache, Chinook and Osprey. He previously held leadership positions on the 757 program, 767 program and in the fabrication division.
Mr. Shanahan is a Royal Aeronautical Society Fellow, Society of Manufacturing Engineers Fellow and American Institute of Aeronautics and Astronautics Associate Fellow. He served as a regent at the University of Washington for over five years.
Mr. Shanahan holds a Bachelor of Science degree in mechanical engineering from the University of Washington and two advanced degrees from the Massachusetts Institute of Technology: a Master of Science degree in mechanical engineering, and an MBA from MIT’s Sloan School of Management.