Admiral Sir Ben Key has formally taken over as First Sea Lord.
He succeeds Admiral Sir Tony Radakin as Royal Navy chief, who himself is taking over as Chief of the Defence Staff.
It was confirmed last month that Adm Key would be appointed First Sea Lord, with the officer also being promoted to a four-star rank as he takes up the role.
Adm Radakin formally handed over command of the Royal Navy to Adm Key during a ceremony on board Nelson's flagship HMS Victory in Portsmouth.
Who is Admiral Sir Ben Key?
Adm Key joined the Royal Navy in 1984 as a university cadet, graduating in physics from Royal Holloway University London.
He has commanded four ships during his time in the service, including the aircraft carrier HMS Illustrious.
The new First Sea Lord's most recent role has been Chief of Joint Operations, during which he was in overall command of Operation Pitting - the UK's evacuation mission from Afghanistan.