FIRST (Fragmentation of Ions Relevant for Space and Therapy) is an experiment aimed at the measurement of double-differential cross sections, with respect to kinetic energy and scattering polar angle, of nuclear fragmentation processes in the energy range between 100 and 1000 MeV/u. The experiment was performed with the SIS accelerator at GSI (Darmstadt, Germany). During August 2011 a first set of data was collected using a 400 MeV/u 12C ion beam on carbon and gold targets. We present a description of the experimental apparatus and some preliminary results from the data acquisition and from the data analysis.