First Sea Lord

First Sea Lord, officially known as First Sea Lord and Chief of the Naval Staff (1SL/CNS), is the title of a statutory position in the British Armed Forces, usually held by an admiral. As the highest-ranking officer to serve in the Royal Navy, the chief is the principal military advisor on matters pertaining to the navy and a deputy to the Secretary of State for Defence. In a separate capacity, the CNS is a member of the Chiefs of Staff Committee and, thereby, a military advisor to the National Security Council, the prime minister and the monarch. The First Sea Lord is typically the highest-ranking officer on active duty of the Royal Navy unless the Chief of the Defence Staff is a naval officer. The post has been vacant since the resignation of Admiral Sir Ben Key in May 2025.