Jan Beneš worked in various blue-collar jobs, for example in crane maintenance for Danly Machine Corporation, before he became a Research Fellow in International House at Harvard University in 1972. After the beginning of the War in Vietnam Jan Beneš tried to join the US Armed Forces, but was refused as too old for regular service. In 1974 he started to work for the Department of Defense, the Defense Language Institute, at Foreign Language Center in Montery, California, as a teacher of Czech language, geography and history. He went through all the training with the Green Berets as a volunteer and participated in many missions, mostly abroad.