The article of record as published may be found at http://dx.doi.org/10.1177/1541931213601202The Habitability Assessment Test (HAT) was designed to evaluate whether Marines exposed to waterborne motion in an amphibious vehicle experience reductions in combat effectiveness. A total of 61 active duty Unites States Marines participated in a within-subjects, repeated measures, quasi-experimental design with counterbalancing to control for order of exposure to waterborne motion of one, two, or three hours. Dependent variables included wrist-worn actigraphy, Stanford Sleepiness Scale scores, marksmanship scores, obstacle course performance, and the switching task from the Automated Neuropsychological Assessment Metric (ANAM) battery. Results showed no statistically significant associations between sleep metrics and the mean radius of impact in the marksmanship test. In contrast, short sleep duration and elevated sleepiness were associated with worse (higher) completion times in the obstacle course. Elevated sleepiness was also associated with lower cognitive throughput, i.e., the number of correct responses per minute, as measured by the ANAM Switching Task. Increased sleep duration was associated with increased throughput, however the trend was not statistically significant. These results suggest that sleep-deprived Marines experienced poorer executive decision making as measured using the ANAM. In addition to showing decrements in combat effectiveness that are associated with their sleep patterns, the current study may provide an early indication of circadian scarring in these young Marines
