  We establish the global existence and uniqueness of classical solutions to
the Cauchy problem for the isentropic compressible Navier-Stokes equations in
three spatial dimensions with smooth initial data which are of small energy but
possibly large oscillations with constant state as far field which could be
either vacuum or non-vacuum. The initial density is allowed to vanish and the
spatial measure of the set of vacuum can be arbitrarily large, in particular,
the initial density can even have compact support. These results generalize
previous results on classical solutions for initial densities being strictly
away from vacuum, and are the first for global classical solutions which may
have large oscillations and can contain vacuum states.
