  Type Ia supernovae (SNIa) remain mysterious despite their central importance
in cosmology and their rapidly increasing discovery rate. The progenitors of
SNIa can be probed by the delay time between progenitor birth and explosion as
SNIa. The explosions and progenitors of SNIa can be probed by MeV nuclear gamma
rays emitted in the decays of radioactive nickel and cobalt into iron. We
compare the cosmic star formation and SNIa rates, finding that their different
redshift evolution requires a large fraction of SNIa to have large delay times.
A delay time distribution of the form t^{-1.0 +/- 0.3} provides a good fit,
implying 50% of SNIa explode more than ~ 1 Gyr after progenitor birth. The
extrapolation of the cosmic SNIa rate to z = 0 agrees with the rate we deduce
from catalogs of local SNIa. We investigate prospects for gamma-ray telescopes
to exploit the facts that escaping gamma rays directly reveal the power source
of SNIa and uniquely provide tomography of the expanding ejecta. We find large
improvements relative to earlier studies by Gehrels et al. in 1987 and Timmes &
Woosley in 1997 due to larger and more certain SNIa rates and advances in
gamma-ray detectors. The proposed Advanced Compton Telescope, with a
narrow-line sensitivity ~ 60 times better than that of current satellites,
would, on an annual basis, detect up to ~ 100 SNIa (3 sigma) and provide
revolutionary model discrimination for SNIa within 20 Mpc, with gamma-ray light
curves measured with ~ 10 sigma significance daily for ~ 100 days. Even more
modest improvements in detector sensitivity would open a new and invaluable
astronomy with frequent SNIa gamma-ray detections.
