With headquarters in New York City at 630 Fifth Avenue, Room 3603, the organization known as the British Security Coordination, or B.S.C., was the keystone of the successful Anglo-American partnership in the field of secret intelligence, counterespionage and special operations.The man chosen by Winston Churchill to set up and direct this crucial effort was Sir William Stephenson, known to the world of espionage as the Man Called Intrepid (see page __). A fighter pilot in the first World War, he had become a millionaire before he was thirty though his invention of the device for transmitting photographs by wireless. The late General Bill Donovan, director of the Office of Strategic Services, said of him: Bill Stephenson taught us all we ever knew about foreign intelligence.Sir William Stephenson put all his papers and much other relevant material at the disposal of H. Montgomery Hyde, a member of his wartime organization who knew him intimately. The result is Room 3603, a unique picture of the British Secret Service in action, and of the remarkable exploits of its brilliant but personally unobtrusive chief in the United States.