The Institute soon started collaborating internationally, in spite of the political isolation of Spain in those years. The foreign visitor who started an active collaboration with INTA was the Hungarian Theodore von Kármán, considered the greatest aeronautics specialist of the century. Von Kármán definitely played a crucial role in the INTA foreign relationships; however, it is worth mentioning Esteban Terradas, who played an important role as president of the first INTA board until his death in 1950.
Due to the important role played by Esteban Terradas in INTA, three months after his death, a decree in which Esteban Terradas was added to the name of INTA was published in the BOE. Even before the creation of INTA, when the Institute was just a project, Esteban Terradas worked with Germany in order to ease materials acquisition for the future engine laboratory.
In 1943, as he explains in a letter written in May of that year to the great mathematician Rey Pastor, he was working on the plans for an aerodynamic tunnel of the Institute. The following year, Terradas was named head of the Engines Department. Terradas’ work was not limited to the presidency of the Board; he had a participated actively in the organization of INTA. Thus, he commissioned the structuring of some new departments, such as Physics (to Julio Palacios) and Chemistry (to Antonio Mora). In these commissions, Terradas stated that they were not academic researches, but rather applied researches; this was only achieved in the latter case.
Terradas’ duty could be labelled as diplomatic. In October 1944 –i.e. before the end of the World War– he started on a long trip, which took more than nine months, throughout the United States. In his trip, he had to "study the possibility of acquiring diverse materials and devices that could be interesting for the Institute", among other purposes. He also studied the possibility of expanding the work of INTA staff to the US, since the staff training was a constant concern for Esteban Terradas.
The result was unequal, although some materials (e.g. three General Electric dynamometers) were acquired, the proposal of sending interns was denied. MIT’s Aeromotors Professor Edward Taylor, one of many with whom he interviewed, gave him the advice of not "doing anything until the political situation was cleared up".
After this denial, Esteban Terradas proposed that it was foreign teachers who visited Spain. Those who witness this period agree on the important role played by Esteban Terradas. As Felipe Lafita wrote, "his personal relationships enabled us to lead the most outstanding international scientists in the various subjects of the exact sciences" to take courses at INTA. Among these outstanding international scientists were Kampé de Feriet, Peres, Milne Thomson, Maurice Roy, Luigi Broglio, Eula, Lorenz, Nobile and, most important, due to the importance and assiduousness of his visits, Theodor von Kármán.
Von Kármán would, in effect, become the best Spanish, or INTA, "ambassador" in the United States, as some of his letters supporting Felipe Lafita, Antonio Pérez-Marín and other aeronautical engineers show. Afterwards, they were invited to visit various aeronautical facilities of that country. On his first visit to Spain, in 1947, von Kármán contacted Esteban Terradas, who invited him back to deliver some lectures a year later. INTA paid him 10,000 pesetas, and accommodation and travelling expenses for these lectures. According to Sánchez Ron, we can say that the relation with Professor Theodore von Kármán "constituted an important aid to facilitate the establishment of relationships with the United States".