The behavior of a chemical tanker (CT) in extreme waves was discussed in detail, that is, in terms of rigid body heave and pitch motions, vertical bending moments (VBMs) amidships, green water, and slamming impacts through the analysis of the experimental data from model tests. Regular wave tests conducted for two wave steepness showed that the increase in wave steepness caused the increase in the asymmetry between hogging and sagging moments and the contribution of green water on deck to the decrease in vertical wave bending moments. Random uncertainty analysis of statistical values in irregular wave tests with various seeds revealed slight experimental uncertainties on motions and VBMs and slightly higher errors in slamming pressure peaks. With the increase in forward speed, experimental uncertainty on slamming pressures at the bow increased. Breather solutions of the nonlinear Schrödinger equation applied to generate tailored extreme waves of certain critical wavelengths showed a good performance in terms of ship response, and it was further verified for the CT.