Johnson's initial sea duty assignment was in VA-66 flying the A-7E Corsair II and deploying in USS Nimitz.

Shore duty assignments include the Command and Staff Course, Naval War College (graduating with highest distinction); Systems Analysis Division (OP-96) of the Office of the Chief of Naval Operations; F/A-18/A-7 readiness officer on the staff Commander Naval Air Force, United States Atlantic Fleet; Joint Chiefs of Staff as head of the European Command/Central Command Branch of the Joint Operations Division (JOD), Operations Directorate (J-3); and Office of the Chairman of the Joint Chiefs of Staff as the executive assistant to the chairman.

His first flag assignment was as the director of operations, plans, and policy (N3/N5) on the Commander in Chief, United States Atlantic Fleet staff.

His previous assignment was commander, United States Sixth Fleet and Naval Striking and Support Forces Southern Europe.

He is also a member of the Energy Security Leadership Council,[1] and sits on the board of directors of Integrian, a surveillance technology company.