Abstract: The Mexican Secret Service under the leadership of Felix A. Sommerfeld, a German naval intelligence officer, successfully recruited agents on both sides of the border in the spring of 1912. The "Sommerfeld organization" thwarted the efforts of Pascual Orozco and his Científico backers to overthrow the government of Francisco I. Madero in 1912. The Mexican Secret Service did this with the help of the U.S. Justice Department and local law enforcement, American business interests in New York, and lobbyists in Washington D.C. Thousands of actual and potential revolutionary recruits ended incarcerated for years. Sommerfeld's organization along the border in 1912 is the largest foreign secret service operation ever mounted on U.S. soil.