  We present an overview of four ab initio axisymmetric core-collapse supernova
simulations employing detailed spectral neutrino transport computed with our
CHIMERA code and initiated from Woosley & Heger (2007) progenitors of mass 12,
15, 20, and 25 M_sol. All four models exhibit shock revival over \sim 200 ms
(leading to the possibility of explosion), driven by neutrino energy
deposition. Hydrodynamic instabilities that impart substantial asymmetries to
the shock aid these revivals, with convection appearing first in the 12 M_sol
model and the standing accretion shock instability (SASI) appearing first in
the 25 M_sol model. Three of the models have developed pronounced prolate
morphologies (the 20 M_sol model has remained approximately spherical). By 500
ms after bounce the mean shock radii in all four models exceed 3,000 km and the
diagnostic explosion energies are 0.33, 0.66, 0.65, and 0.70 Bethe (B =
$10^{51}$ ergs) for the 12, 15, 20, and 25 M_sol models, respectively, and are
increasing. The three least massive of our models are already sufficiently
energetic to completely unbind the envelopes of their progenitors (i.e., to
explode), as evidenced by our best estimate of their explosion energies, which
first become positive at 320, 380, and 440 ms after bounce. By 850 ms the 12
M_sol diagnostic explosion energy has saturated at 0.38 B, and our estimate for
the final kinetic energy of the ejecta is \sim 0.3 B, which is comparable to
observations for lower-mass progenitors.
