In this paper, the unstructured-grid flow solver, FUN3D, is used to compute the aerodynamic performance of F-15. A half model of F-15 with 14 million grid points is used for both steady and unsteady computations. The Detached Eddy Simulation (DES) method based on the Spalart-Allmaras (SA) turbulence model is used in the unsteady computation of the F-15 with high angle of attack. Computational results for the transonic steady cases of the F-15 vertical tail and the benchmark case of a cylinder in a cross flow are presented, showing excellent agreement with other numerical results and experimental measurements in the literature. Furthermore, unsteady pressure fluctuations on the F-15 vertical tail at a high angle of attack (22°) are computed. The effect of the far field turbulence on the power spectrum of the pressure is studied, and the optimal turbulence level is determined to capture the dominant regime of the power spectrum of the pressure measured in wind tunnel tests. The FUN3D computation is thus expected to provide reliable pressure data for the prediction of the buffeting response of the F-15 vertical tail.