A more comprehensive comparison of responses to regular waves is given in this chapter for a 6500TEU-containership. It shows results of model experiments, of a linear strip method, a Green function method including nonlinear corrections, a linear and a fully nonlinear Rankine source method, and a RANS method. Compared are ship motions as well as linear and nonlinear section forces and moments in three transverse sections. The ship speed is varied between 0 and 15 knots. Only longitudinal (head and following) waves are covered; the maximum wave height (in full scale) is 10 m. Results show that motions can be well predicted by linear three-dimensional methods, but accurate section loads in steep waves require nonlinear computing methods. Apparently, both experiments and nonlinear computational methods have difficulties with loads in steep waves, but nonetheless carefully computed results are of sufficient accuracy for practical application.