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INTRODUCTION: Military divers and tactical aviators face numerous environmental hazards making each operation a calculated risk. Hypercapnia, elevated CO2 in the arterial blood (PaCO2), is one of the stressors that can result in impairments in operator neurological status, increase the probability of an accident and present a significant risk to the operator. The following two studies explore the direction and magnitude of the effect of low-level exposures to CO2 on tracking performance (TP), reaction time (RT) and executive function (EF). METHODS: Study 1: Thirty-five active-duty Student Naval Aviators (SNAs) (M = 24.11 years, SD = 2.14) performed two iterations of the Cognitive Assessment of Aviation Performance and Evaluation of State (CAAPES), while breathing four normobaric CO2 concentrations, 1.0%, 2.5%, 4.0%, 5.5%, delivered via an MBU-20/P flight mask, for 15-minutes in each condition. Study 2: Twenty-five active-duty (SNAs) (M = 23.36 years, SD = ±1.68) performed either two or three iterations of a Stroop Task and a Go/No-Go Task while breathing normobaric CO2 concentrations, 0.04%, 1%, 2.5%, and 4%, delivered via Interspiro MKII Divator Mask for 15 minutes in each condition. RESULTS: Transcutaneous (PaCO2) increased in participants across all four of their respected CO2 exposures. The ANOVA conducted on the tracking component of CAAPES without the subtasks showed, f (1.69, 28.78) = 4.39, p = 0.027, partial eta square = 0.21. TP peaked at 4.0% CO2. Repeated Measures ANOVA of the Stroop Effect RT scores showed a significant effect, (F (3, 72) = 3.494, p = .020). Participants Stroop accuracy percentage showed no effect, (F (72,3) = .319, p = .812). A Repeated Measures ANOVA of average number of failed "No-Go" responses showed no effect, (F (69, 3) = 1.106, p = .353, ηp2 = .046). RT Performance Peeked at 2.5% and 4.0% CO2. CONCLUSION: The stimulating and arousal effects of CO2 significantly improved TP on CAAPES and RT on Stroop and Go/ No-Go. CO2 exposure did not negatively affect EF as measured by Stroop and Go/No-Go. Across all metrics high PaO2 conditions were associated with better performance as predicted by the Yerkes-Dodson Law and the Bohr Effect. Learning Objectives 1. Why is CO2 a common stressor divers and aviators face operationally? 2. How executive and non-executive function cognitive processing is affected by CO2. 3. How CO2 affects performance through the Yerkes Dodson Law and the Bohr Effect. [ABSTRACT FROM AUTHOR]