 Segre began working at his father's construction business, only to have his career and education interrupted by the outbreak of World War II.Stationed in Naples on 8 September 1943, when the armistice was announced, Segre immediately voiced opposition to the German troops occupying the city – and participated in the Four days of Naples.When allied troops arrived, he made himself available to the US command, and after a brief training in Tunisia, parachuting into the Canavese, he became an official liaison between the Office of Strategic Services (OSS) – precursor to the modern CIA – and partisan groups working in the Piedmont.