The Minister of Defence is the Administrative Head of the Defence Ministry of the Imperium.
The Minister is also known as the High Imperial Marshal. The office of the Imperial Minister of Defence is not in the chain of command.
The Minister of Defence is appointed by the Emperor and reports directly to him. Note that the office of Minister of Defence attracts the noble rank of Duke.
The Minister is in charge of advising the Emperor on military affairs, evaluating the general state of the Imperial military, and supervising long-term military planning, research, and development.
The Minister of Defence is based at the Imperial Capital, has a wing of the Imperial Palace for his headquarters and sits on both the Admiralty Board and the Army Board.