This paper presents a new scheme to implement the iterative physical optics (IPO) approximation with edge diffraction for the scattering from large perfectly-conducting objects, for which, multiple reflections occur. The use of the electric field integral equation (EFIE) discretized by the Galerkin method of moments (MoM) with Rao-Wilton-Glisson basis functions leads to solving a linear system. The characteristic basis function method (CBFM) needs to invert the self-impedance sub-matrices to calculate the primary basis functions (PBFs). To accelerate this stage, these sub-linear systems are directly solved from the physical optics (PO) approximation. In addition, to improve the precision of PO, the EFIE-PO self-impedance matrix is derived analytically. This avoids to apply the magnetic field integral equation (MFIE), for which its principal value is related to PO. Numerical results showed that the resulting algorithm, CBFM-PO, predicts inherently the edge diffraction. A domain decomposition method is able to split up the geometry into blocks, for which either the PO or a LU decomposition is applied according to the sub-geometry. To accelerate the coupling steps, the adaptive cross approximation (ACA) is also implemented, and the resulting method is tested on different targets having a curvature and producing multiple reflections. The numerical results show that EFIE-CBFM-PO is more accurate than the conventional EFIE-CBFM-POJ (based on Jakobus et al. work), specially for objects with curvature.