Between 2008 and 2018, at least 380 high-ranking Pentagon officials were hired by top defense contractors after leaving public office, according to the Project On Government Oversight (POGO) – including 25 generals, 9 admirals, 43 lieutenant generals and 23 vice admirals.
https://www.pogo.org/report/2018/11/brass-parachutes/
The number of instances of the revolving door is certainly much higher than what we found using publicly available sources since those sources largely rely upon self-reporting by the companies and individuals. A 2006 Government Accountability Office survey of contractors and Internal Revenue Service data—the most recent government review available—found that 52 contractors employed 2,435 former Department of Defense senior and acquisition officials who had “previously served as generals, admirals, senior executives, program managers, contracting officers, or in other acquisition positions which made them subject to restrictions on their post-DOD employment.”2