  We consider the nu_mu to nu_e oscillation measurements that would be possible
at upgraded 1 GeV and multi-GeV conventional neutrino sources driven by future
megawatt-scale proton drivers. If these neutrino superbeams are used together
with detectors that are an order of magnitude larger than those presently
foreseen, we find that the sensitivity to nu_mu to nu_e oscillations can be
improved by an order of magnitude beyond the next generation of accelerator
based experiments. In addition, over a limited region of parameter space, the
neutrino mass hierarchy can be determined with a multi-GeV long baseline beam.
If the Large Mixing Angle MSW solution correctly describes the solar neutrino
deficit, there is a small corner of allowed parameter space in which maximal
CP-violation in the lepton sector might be observable at a 1 GeV medium
baseline experiment. Superbeams with massive detectors would therefore provide
a useful tool en route to a neutrino factory, which would permit a further
order of magnitude improvement in sensitivity, together with a more
comprehensive check of CP-violation and the oscillation framework.
