Admiral Zambellas talks to members of HMS Illustrious' Air Department on 23 January

As the First Sea Lord and Chief of Naval Staff, Adm Zambellas is the Royal Navy's professional head and Chairman of the Navy Board.

He is responsible to Secretary of State for the fighting effectiveness, efficiency and morale of the Naval Service, and supports the Secretary of State in the management and direction of the Armed Forces.

As a member of the Chiefs of Staff Committee, he advises on maritime strategy and policy, and has a collective responsibility for providing strategic direction to the department, managing performance and ensuring that Defence delivers the required outputs. 

He takes over from Sir Mark at a time when there are numerous changes in post in the upper echelons of the MOD as announced by Mr Hammond.

Air Marshal Sir Andrew Pulford will take over as the head of the RAF from Air Chief Marshal Sir Stephen Dalton in July; Air Chief Marshal Sir Stuart Peach will become Vice Chief of the Defence Staff in May 2013; and an announcement on the new Chief of the Defence Staff to take over from General Sir David Richards will be made next month.