Proton accelerators such as the SPS provide essentially nm beams from the decay of p's and K's, produced when the extracted proton beam hits a target. These 'parent' particles are focused towards the detector and left to decay in a tunnel to produce muons and nm . The muons and all remaining hadrons are dumped at the end of the decay tunnel leaving only the neutrinos travelling towards the detector target. The ICARUS 600 t sensitivity to long baseline neutrino oscillation is limited by statistics. Therefore, a complete study of the long baseline neutrino sector will be accomplished only with a larger detector mass of the order of several kilotons. Nevertheless the use of the ICARUS 600-ton detector will be able to provide preliminary fundamental results during the beam operation start-up.