The sleep, circadian, and cognitive performance consequences of watchkeeping schedules in submariners: A scoping review

Watchkeeping schedules are essential for maintaining submarine operations, but come with human risk factors including, disrupted sleep, circadian misalignment, and cognitive deficits. There is now an emerging literature examining the strengths and weaknesses of submarine watchkeeping schedules trialled in the field and under simulated laboratory conditions. The aim of this scoping review was to summarise this literature. A systematic search of peer-reviewed journal articles and industry reports listed in MEDLINE, PsychINFO, PubMed, Scopus, Embase and Google Scholar undertaken in May 2023 returned 7298 papers. Following screening procedures, 13 studies were identified for inclusion. The findings revealed that sleep was sufficiently preserved regardless of watchkeeping schedule (total sleep time = 5.46-7.89 h), circadian misalignment was greater for non-24 h schedules, and longer off-watch periods were associated with better cognitive performance. Taken together, when comparing between watchkeeping schedules, the present findings suggest that the 4 h-on/8 h-off and 8 hon/16 h-off schedules may be a good compromise when balancing human risk factors and operational demands. However, submarines are complex and challenging environments to study and there is a need to expand the literature. More research comparing watchkeeping schedules is needed. Future studies should focus on cognitive performance measures, such as problem-solving, prioritisation and executive decision-making to address present shortcomings, and an examination of sleep and circadian countermeasures to assist with adaptation either initiated pre-deployment or by modifying the submarine environment itself should be considered.