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

Summary 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.