We describe a family of genus one fibered Calabi-Yau threefolds
with fundamental group Z/2. On each Calabi-Yau Z in the family we
exhibit a positive dimensional family of Mumford stable bundles whose
symmetry group is the Standard Model group 5C/(3) x SU(2) x U(l)
and which have C3 = 6. We also show that for each bundle V in our
family, C2(Z) — C2{V) is the class of an effective curve on Z. These
conditions ensure that Z and V can be used for a phenomenologically
relevant compactification of Heterotic M-theory.