  We investigate in this paper the core-collapse supernova explosion mechanism
in both one and two dimensions. We verify the usefulness of neutrino-driven
overturn (``convection'') between the shock and the neutrinosphere in igniting
the supernova explosion. The 2-D simulation of the core of a 15$\mdot$ star
that we present here indicates that the breaking of spherical symmetry may be
central to the explosion itself and that a multitude of bent and broken fingers
is a common feature of the ejecta. In 2-D, the steady-state shock radius is
larger than its value in 1-D by 30\%--100\%. The critical condition for
explosion is thereby relaxed. Since supernovae are driven by neutrino heating,
they are coronal phenomena, akin to winds, though initially bounded by an
accretion tamp. Neutrino energy is pumped into the supernova during the shock's
propagation through the inner many thousands of kilometers and not
instantaneously. Curiously, just after the explosion is triggered, the matter
that will eventually be ejected is still bound. The high-speed fingers that
emerge from the core seem a natural explanation for the nickel bullets seen in
87A and the shrapnel inferred in some supernova remnants. Within 100 ms of the
explosion, a strong, neutrino-driven wind is blowing outward from the
protoneutron star.
