William S. Castle, Esq., formerly served as Principal Deputy General Counsel, having been so appointed by the Secretary of Defense in August 2017.  He also served as Acting General Counsel and the official performing the duties of the General Counsel from August 2017 to August 2018. 

In December 2019, Mr. Castle was awarded the Department of Defense’s Medal for Distinguished Public Service.  This is the highest award presented by the Secretary of Defense to a non-career federal employee for exceptionally distinguished service.  

Previously, Mr. Castle was Minority General Counsel to the Senate Armed Services Committee, Chief Counsel in Senator Orrin Hatch's Office of the Senate President Pro Tempore, and Senator Hatch’s Senior National Security Counsel.

Mr. Castle received his Bachelor of Arts in Political Science from Brown University in 1993 and his Juris Doctorate from the University of Pennsylvania Law School in 1999. His work has been published in the Harvard Journal of Law and Public Policy. Mr. Castle is admitted to practice law in New Jersey and the District of Columbia.