The creation of the Union of South American Nations (USAN) aroused expectations about joint development and production of military aircraft in South America. However, political divergences, technological asymmetries and budgetary problems made projects canceled. Faced with the impasse, this article approaches features of two military aircraft development experiences and their links with the regionalization processes to extract elements that help to account for the problems faced by USAN. The processes of adoption of the F-104 and the Tornado in the 1950s and 1970s by countries that later joined the European Union are analyzed in a comparative perspective. The two projects are compared about the political and diplomatic implications (mutual trust, military capabilities and regionalization) and the economic implications (scale of production, value chains and industrial parks). We argue that both processes generated convergence, though countries involved already shared threat perceptions and a military alliance, which compelled them to cooperation. Thus, the successful joint development of military aircrafts within USAN would require a previous level of convergence not yet achieved.