  We establish the equivalence of the Gimon-Polchinski orientifold and F-theory
on an elliptically fibered Calabi-Yau three fold on base $CP^1 \times CP^1$ by
comparing the gauge symmetry breaking pattern, local deformations in the moduli
space, as well as the axion-dilaton background in the weak coupling limit in
the two theories. We also provide an explanation for an apparent discrepancy
between the F-theory and the orientifold results for constant coupling
configuration.
