The G-Stack collaboration was a unique network of European laboratories interested in cosmic rays as a source of particles. The network was established in the mid-1950s in order to carry out a balloon flight aimed at using nuclear emulsions to investigate the nature of K mesons. The experiment was significant for the physics of the period, not only because of the scientific results it achieved, but also because it represented an experiment of transition from one epoch to another, from "small science" to "big science," from cosmic rays to accelerators. Launched from northern Italy in 1954, it was also the first strong response to the idea of establishing an international collaboration among European countries in the field of particle physics, with more than thirty authors signing the papers under the collective name of "G-Stack collaboration." An excellent example of knowledge circulation in a European framework, the G-Stack collaboration left a strong heritage for the biggest scientific European institutions and for the reconstruction of Italian physics after the Second World War.