Oscillation of underwater vehicles (particularly submarines) in littoral zones, where water is more likely to be stratified, generates particular waves that can reveal information about size, speed and the depth of the vehicle. We studied the mechanism behind the generation of these waves and their interactions. For a steadily translating and sinusoidally oscillating disturbance in a two-layer fluid, up to eight waves may appear on the water surface/interface. Unlike in homogeneous fluid, nonlinear resonance can occur between these eight waves. We theoretically found, and numerically validated, that existence of stratification along with second-order nonlinearities can result in generation of a series of new waves that can travel away or toward the disturbance.