We report the first observation of objects moving through He II with equilibrium drift velocities v beyond the Landau critical velocity vc,for roton creation. With T about 0.4 K, P = 25 bar, F =2 kV/cm, (v - vc) for negative ions is larger than a theoretical prediction by a factor of about 10^5. The vortex-ring nucleation rate is found to decrease with F above 300 V/cm, thus resolving apparent inconsistencies between earlier experiments.