Information:  - The Special Air Service (SAS) is a special forces unit of the British Army. The SAS was founded in 1941 as a regiment, and later reconstituted as a corps in 1950. The unit undertakes a number of roles including covert reconnaissance, counter-terrorism, direct action and hostage rescue.  - An office created in the Private Secretary's Office of the Royal Household of the Sovereign of the United Kingdom in 2004. The first office-holder was Brigadier Jeffrey Cook, a former Special Air Service (SAS) officer. He served until 2008.  - Brigadier Jeffrey Cook , OBE MC , was appointed Director for Security Liaison in the Royal Household of the Sovereign of the United Kingdom in 2004 . He retired in 2009 and is now Managing Director of the Morgan Aquila Group . Cook was born in 1954 and later joined the Devonshire and Dorset Regiment . He trained as a parachutist , and served in Balkans and elsewhere as an officer of the Special Air Service Regiment . The Director for Security Liaison is a new addition to the Private Secretary 's Office in the Royal Household of the Sovereign of the United Kingdom . Brigadier Jeffrey Cook is the first holder of the post . The Private Secretary has general oversight of security , though the Master of the Household is also involved , and the Keeper of the Privy Purse has responsibility for the ceremonial bodyguards .    Given the information above, choose from the list below the object entity that exhibits the relation 'military branch' with the subject 'jeffrey cook '.  Choices: - british army  - regiment  - special air service
Answer:
british army