Question: In what capacity did British Army intelligence officer Derek Knee serve in World War II to the Field Marshall nicknamed "Monty" and the "Spartan General"?

Context paragraphs:
Stencil Subtractor: The Stencil Subtractor frame was a ciphered text recyphering tool that was invented by British Army Intelligence Officer and cryptographer John Tiltman and was ready for trial by April 1941 but was not adopted officially by the British Forces until March 1942, and not brought into service until June 1943.  It replaced the venerable and vulnerable Subtractor tables which had been previously used to encipher British military (Military communications) and civilian codes during World War II.

Carter W. Clarke: Carter W. Clarke (died 1987) was a U.S. Army intelligence officer and brigadier general.  He was the military intelligence officer who prepared intercepted Japanese Magic cables for U.S. officials.  He also headed a War Department investigation into the role that military intelligence leading up to the Japanese attack on Pearl Harbor.  He died of a heart attack in 1987 at his home in Clearwater, Florida.

Derek Knee: Derek Knee (22 October 1922 – 18 March 2014) was a British Army intelligence officer during World War II who was the interpreter and translator for Field Marshal Sir Bernard Montgomery, commander of the Anglo-Canadian 21st Army Group, at the German surrender at Lüneburg Heath in Germany on 3 May 1945.

Edwin L. Sibert: Edwin Luther Sibert (March 2, 1897 – December 16, 1977) was a United States Army officer with the rank of Major General and served as intelligence officer during World War II and post-war Europe where he assisted in the creation of the Gehlen Organization.  He would return to the United States and briefly serve in the Central Intelligence Group, the forerunner of the modern CIA.  He was the son of Major General William L. Sibert and the brother of Major General Franklin C. Sibert.  A graduate of the United States Military Academy in 1918, he would receive the Distinguished Service Medal three times for his service during World War II and the Cold War.

Gilbert Clayton: Brigadier Sir Gilbert Falkingham Clayton (6 April 1875 – 11 September 1929), was a British army intelligence officer and colonial administrator, who worked in several countries in the Middle East in the early 20th century.  In Egypt, during World War I as an intelligence officer, he supervised those who worked to start the Arab Revolt.  In Palestine, Arabia and Mesopotamia, in the 1920s as a colonial administrator, he helped negotiate the borders of the countries that later became Israel, Jordan, Syria, Saudi Arabia and Iraq.

Oscar Koch: Oscar W. Koch (January 10, 1897, Milwaukee, Wisconsin - May 16, 1970, Carbondale, Illinois) was a brigadier general in the U.S. Army and the Third Army intelligence officer (G-2) while the army was commanded by General George S. Patton in World War II.

Westland Lysander: The Westland Lysander (nickname the 'Lizzie') was a British army co-operation and liaison aircraft produced by Westland Aircraft used immediately before and during the Second World War.  After becoming obsolete in the army co-operation role, the aircraft's exceptional short-field performance enabled clandestine missions using small, unprepared airstrips behind enemy lines to place or recover agents, particularly in occupied France with the help of the French Resistance.  British army air co-operation aircraft were named after mythical or historical military leaders; in this case the Spartan general Lysander was chosen.

Counterintelligence Corps: The Counter Intelligence Corps (CIC) was a World War II and early Cold War intelligence agency within the United States Army.  Its role was taken over by the U.S. Army Intelligence Corps in 1961 and, in 1967, by the U.S. Army Intelligence Agency.  Its functions are now performed by the United States Army Intelligence and Security Command and by counterintelligence agents assigned to Army tactical units.  The National Counter Intelligence Corps Association (NCICA), a veterans' association, was established in the years immediately following World War II by Military Intelligence agents who had served in every area of military and domestic operations.  The organization meets annually.  Its newsletter, the "Golden Sphinx", is published quarterly.

Hugh Toye: Colonel Claude Hugh Toye MBE (29 March 1917- 15 April 2012) was a British Army intelligence officer who worked in India and Burma during World War II.  Working in the Combined Services Directorate of Intelligence, Toye was tasked with interrogation of captured troops of the Japanese army and the Indian National Army.  Toye's work recording the history of the INA,"The Springing Tiger" published in 1959, was one of the first authoritative histories on the army penned by a western scholar.  After the war Toye worked with the British army in South-east Asia.  He worked in various capacities in Burma, Laos and Hong Kong and Bangkok in between short spells in Europe.  He earned a PhD from Nuffield College Oxford in late 1960s.  Toye retired from the army in 1972.

Bernard Montgomery: Field Marshal Bernard Law Montgomery, 1st Viscount Montgomery of Alamein, ( ; 17 November 1887 – 24 March 1976), nicknamed "Monty" and the "Spartan General", was a senior British Army officer who fought in both the First World War and the Second World War.

Supporting paragraphs: Derek Knee Bernard Montgomery
Answer: interpreter and translator