Major General Sir Stewart Graham Menzies, KCB, KCMG, DSO, MC (/ˈmɪŋɪz/ ⓘ; 30 January 1890 – 29 May 1968)[1] was Chief of MI6, the British Secret Intelligence Service (SIS), from 1939 to 1952, during and after the Second World War.

But Menzies' father was dissolute, never established a worthwhile career, and wasted his share of the family fortune; he died of tuberculosis in 1911 in his early 50s, leaving only a minimal estate.

[14] This forgery is considered to have been instrumental in the Conservative Party's victory in the United Kingdom general election of 1924, which ended the country's first Labour government.

Extensive breaches of Nazi Enigma signals gave Menzies and his team enormous insight into Adolf Hitler's strategy, and this was kept a closely held secret, not only during the war, but until as late as 1974.

The Nazis had suspicions, but believed Enigma to be unbreakable, and never knew during the war that the Allies were reading a high proportion of their wireless traffic.

[18] Menzies kept Prime Minister Winston Churchill supplied daily with important Ultra decrypts, and the two worked together to ensure that financial resources were devoted toward research and upgrading technology at Bletchley Park, to keep pace with Nazi coding refinements, as well as directing talented workers to the massive effort, which employed nearly 10,000 workers by 1945.

Bletchley's efforts were decisive in the battle against Nazi submarine warfare, which was severely threatening trans-Atlantic shipping, particularly in the first half of 1943.

[19] Menzies has been suspected as being involved with the assassination, on 24 December 1942, of François Darlan, the Vichy military commander who defected to the Allies in Algeria.

British historian David Reynolds noted in his book, In Command of History, that Menzies—who rarely left London during the war—was in Algiers around the period he was killed, making SOE (Special Operations Executive) involvement seem likely.

[20] Menzies, who was promoted to major-general in January 1944, also supported efforts to contact anti-Nazi resistance, including Wilhelm Canaris, the anti-Hitler head of Abwehr, in Germany.

Cave Brown insists that Menzies's primary criteria were whether the applicants were upper-class former officers and recommended by another government department, or else were known to him personally.

"[22] After 43 continuous years of service in the British Army, Menzies retired to Bridges Court in Luckington in rural Wiltshire at 62 in mid-1952.

His success at SIS was not limited to adeptness at bureaucratic intrigue, a virtual necessity in his position; Menzies' efforts as chief had a major role in winning the Second World War, and certainly earned Churchill's trust, as evidenced by nearly 1,500 meetings with the prime minister during its duration.