<p>Noninvasive vagus nerve stimulation provides a promising tool for supporting performance under demanding conditions, particularly during sleep deprivation. This study investigated the effects of transcutaneous auricular vagus nerve stimulation and stimulation intensity on vigilance, sustained attention, response inhibition, self-reported mood, and sleepiness in military conscripts during a 24-h training period that included total sleep deprivation. Forty-eight male conscripts completed the study. Vigilance was assessed using the psychomotor vigilance task and sustained attention and response inhibition with the sustained attention to response task. Before the stimulation, participants adjusted the stimulation intensity individually. The stimulation duration was 4&#xa0;min. For the stimulation group (<i>n</i> = 24), the intensity ranged from 12 to 26&#xa0;mA. In the sham group (<i>N</i> = 24), stimulation was ramped down to 0&#xa0;mA during the first minute. Vigilant attention decreased with prolonged wakefulness in both groups. However, during the early morning hours at 5 am and 7 am, this impairment showed modest attenuation with increasing stimulation intensities; higher intensities were associated with smaller decrements in vigilance. No effects of stimulation were found on response inhibition. The response inhibition task is more motivationally salient than the simple vigilance task, and the impact of sleep deprivation can be obscured by strategic slowing of responses to minimize errors. Also, higher stimulation intensity was associated with a smaller shift toward negative emotional valence measured after the response inhibition task. Transcutaneous auricular vagus nerve stimulation shows potential to support vigilance during sleep deprivation in monotonous tasks, such as radar monitoring and surveillance.</p>