Chief of the Defence Staff (United Kingdom)

Chief of the Defence Staff (CDS) is the title of the professional head of the British Armed Forces and the most senior uniformed military adviser to the Secretary of State for Defence and the prime minister of the United Kingdom, and also meets regularly with the monarch. The CDS is based at the Ministry of Defence and works alongside the Permanent Under-Secretary of State for Defence, the ministry's senior civil servant.

Source: Wikipedia — Chief of the Defence Staff (United Kingdom) (CC BY-SA 4.0)