He also attended the United States Command and General Staff Officer Course in 1992, attaining a master's degree in Military Art and Science.

Part of his responsibility was to deal with organisational changes due to the suspending of the Dutch draft and the transformation of his Group into a professional unit.

Having been promoted a full colonel in 1997 Bertholee was assigned to the Fire Support Training Center as commanding officer.

After returning to The Netherlands in September he was made head of the International Planning department of the Dutch Defense Staff.

Effective 1 February 2005 Bertholee was promoted major general and assigned Director of the Operational Preparedness Control Board (DOAG).