Results of investigations of the generation of subnanosecond runaway electron beams and x radiation in gas diodes at elevated pressures are presented. The energy distributions of runaway electron beams generated in air at atmospheric pressure and the amplitude and duration of beam current pulses downstream of the foil have been measured, and also the mechanism of generation of a runaway electron beam has been analyzed. To record the beam current pulses, a collector which provided ~50-ps time resolution and a Tektronix TDS6604 real-time oscilloscope were used in the experiment. It has been shown that the new experimental data and model predictions confirm in the main the results earlier obtained at the Institute of High Current Electronics of the Russian Academy of Sciences Siberian Division. Evidence is cited that the key statements of L. P. Babich are erroneous.