Between 1945 and 1948, he played a leading role in the clandestine immigration enterprise in Palestine, commanding four Aliyah Bet ships: Knesset Israel, the Exodus 1947, Atzma'ut and Kibbutz Galuyot. After the establishment of the State of Israel, Harel studied mechanical engineering at MIT in the United States. Just before he finished his studies, Moshe Dayan, as Chief of Staff, called him back to Israel to investigate the Lavon Affair and made him head of Unit 131, an Israel Defense Forces intelligence unit.[1]