  We examine the effect of uniform ambient magnetic fields on the evolution of
supernova-driven blast waves into a homogeneous ambient ISM in thermal
equilibrium. Using the Pencil Code we simulate high resolution nonideal
magnetohydrodynamic simulations in 3D. We find that supernova blast waves are
sensitive to plane-parallel magnetic fields of strength in excess of 1 $\mu$G
for ambient gas number density 1 cm$^{-3}$ . Perpendicular to the field, the
inward magnetic pressure gradient induces retrograde mass accretion in the wake
of the primary shock front. Subsequently, we find that the primary shockwave
expands faster perpendicular to the field, but with reduced momentum, while the
remnant core is subject to magnetic confinement. This leads to a decrease in
fractional volume of hot gas but also an increase in the density and
temperature of hot gas in the magnetically confined remnant. The magnetic
pressure gradient behind the shock front generates enhanced regions favourable
to UV- heating and thus reduces net radiative losses. Although the presence of
a strong uniform magnetic field can reduce momentum early on, and hence
residual kinetic energy, it increases the efficiency of residual total energy
injection by the SN into the ISM by up to 40% within 1 Myr.
