The impact of a 20-h rotating watch schedule on cognitive and mood states in submarine operations.

This is the first study to provide valuable insights into the effects of the Israeli Navy's 20-h rotating watch schedule on submariners' alertness, mood states, risk-taking behaviours, and sleep. Specifically, we assessed the impact of the non-circadian-aligned schedule on cognitive performance, mood, and behavioural outcomes in a highly controlled submarine environment. A total of 20 male submariners participated in an at-sea mission, where their cognitive performance, mood states, risk-taking propensity, and caffeine consumption were measured. A psychomotor vigilance task (PVT) assessed alertness, the propensity for risky behaviour (Evaluation of Risks Scale) measured risk-taking behaviours, and the Profile of Mood States evaluated mood disturbances. Actigraphy was used to monitor sleep times. Data were analysed according to seven watch schedule segments. Submariners slept a mean (standard error of the mean [SEM]) of 8.3 (0.2) h/24 h, fragmented into 3.7 (0.8) h epochs. Caffeine consumption decreased at sea (mean [SEM] 149.3 [6.0] mg) compared to land (mean [SEM] 205.5 [7.2] mg; p = 0.027). In the PVT, premature responses significantly increased during Watch VI (5:00-8:00 p.m.) and Watch VII (8:00 p.m.-12:00 a.m.; p = 0.014). In the mood subscales, tension was significantly higher during Watch II (4:00-8:00 a.m.; p = 0.002), indicating greater stress. Risk-taking propensity significantly increased during afternoon shifts (p = 0.050). The 20-h watch schedule led to fragmented sleep, reduced alertness in the evening, worsened mood states in the early morning, and increased risk-taking propensity in the afternoon. These findings suggest the need for the Israeli Navy to establish evidence-based caffeine guidelines and optimise the watch schedule to improve submariners' sleep, performance, and overall well-being.