Koninklijke Landmacht

The submarine working and living environment is an isolated, confined, and extreme (ICE) environment where a continuous on-watch is required to fulfill the tactical objectives. The current study examined whether a physiological and behavioral adjustment to an operational watch standing scheme occurred in terms of hormonal secretion (i.e., melatonin and cortisol) and sleep during a 67-day undersea mission. The crew followed a strict scheme of watch-on blocks at 0:00-06:00 h and at 12:00-18:00 h (group 1, diurnal sleep group) or watch-on blocks at 06:00-12:00 h and 18:00-24:00 h (group 2, nocturnal sleep group). We sampled saliva during the operational blocks over a 24-h period at day 55 of the mission and collected sleep actigraphy data during the entire mission in 10 participants. Sleep showed a biphasic split pattern with significantly unequal distributions of total sleep time (TST) and sleep efficiency (SE) between the two sleeping blocks, i.e., one long and one short sleep bout. Melatonin secretion showed no adjustment at the end of the mission to the watch standing blocks, following an endogenous circadian rhythm independent from the social zeitgebers with indications of a phase shift. Cortisol secretion however matched the biphasic work-sleep shift routine. Human physiology does not fully obey operational needs and there are differences in adjustment between melatonin and cortisol. A watch standing schedule that provides a balance between physiology and operationality still needs to be established. The potential adaptation effects of bright light therapy and melatonin supplementation should be investigated in future research.NEW & NOTEWORTHY The current study has a unique character due to the field context in which the data were collected. Data on long-term submarine missions are scarce and valuable in terms of operational and ecological validity. Moreover, the results are important both from a scientific and operational point of view, showing that human physiology does not fully obey operational needs and that there are differences in adjustment dependent from the type of circadian hormone.

We investigate the benefits of on‐site printing at remote geographic locations, where access to spare parts is intermittent and supplies are replenished at fixed intervals. Organizations typically have no solution to spare parts shortages other than expensive expediting orders, or waiting for a part to arrive with the next replenishment. We investigate whether on‐site three‐dimensional (3D) printing of spare parts can bring relief. Our work extends dual‐sourcing literature with fixed order cycles by considering two emergency supply options: expediting regular parts and 3D printing lower quality parts. We model the replenishment and emergency supply decisions as a Markov decision process and find that the optimal inventory control policy consists of two thresholds that control when to expedite, when to print and when to wait for regular parts via the next replenishment. We apply our model to a case study of the Royal Netherlands Army (RNLA) for her United Nations peacekeeping mission in Mali. Our results show that on‐site 3D printing, much more so than expediting, leads to large operational cost savings through on‐site inventory reductions and increased asset availability, thus increasing the ability of the RNLA to operate in remote locations. These results extend to many other organizations that operate in remote locations, for example, those in the mining and offshore industry.

IntroductionOveruse injuries often start with a musculoskeletal complaint, which can progress over time to an injury. Little or no information is known about the development and severity of overuse injuries in military recruits. This study describes the musculoskeletal complaints in Dutch military recruits during their basic training and examines potential predictive factors for dropout due to injury.MethodsIn this prospective cohort study, Dutch military recruits reported complaints of the lower body weekly using a Numeric Rating Scale (NRS) pain score chart during their basic training. Number, location and severity of complaints during each of the first 12 weeks of basic training were analysed.ResultsOf the 930 recruits, 61% reported an NRS pain score of 3 or higher and 34% reported an NRS pain score of 5 or higher at least once. Complaints were mostly reported in the foot and ankle region and least reported in the upper leg region. Injury dropouts (11%) showed significantly higher proportions of complaints and higher maximal pain scores throughout most weeks of basic training. The maximal NRS pain score of the first two weeks was the strongest predictor of dropping out due to injury.ConclusionsRecruits who drop out due to injury report more severe complaints throughout basic training. Focusing on musculoskeletal complaints in the first phase of training seems helpful to identify recruits who are at risk of developing an injury.