The article presents correspondence from December 1957 between the head of the Legal Service of the High Authority of the European Coal and Steel Community (ECSC), the French member of the Conseil d'Etat, Michel Gaudet, and his friend, the American lawyer Donald Swatland, which sheds new light on what is considered to be "the birth of EEC law": the landmark decisions of the Court of Justice in Van Gend and Loos (5 February 1963) and Costa v. ENEL (15 July 1964), in which the Court laid the basis of two areas of its "constitutional doctrine", the direct effect of Treaty provisions and the primacy of EU law (to give it its current name) over all conflicting national rules including constitutional ones. The correspondence shows that the Court's decisions should be seen as the result of a mobilization strategy led by the Legal Service of the European Executives to secure the advent of the future United States of Europe.