F-theory and the Gimon-Polchinski Orientifold

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.