The population of individuals who serve in the US military is comprised of officers and enlisted personnel who are relatively young in age. Demographically, the average age of officers is 35, while the average age of enlisted personnel is approximately 27 years of age. Nearly one-half (48.8%) of the enlisted personnel are 25 years old or younger in contrast to 13.3% of the officers (“2012 Demographics: Profile of the Military Community,” [1]). This demographic structure highlights the increased need for good-quality sleep for these younger individuals, which, according to a recent consensus report, may be 9 or more hours of sleep per night to promote optimal health [78]. Despite this physiological need, however, it is well documented that individuals who serve in the military continually experience sleep deprivation and elevated fatigue levels [47, 48]. All three components of good sleep (timing, duration, and quality) are challenged in the military environment. During the last two decades, numerous studies conducted at the Naval Postgraduate School have documented the sleep patterns of active duty service members (e.g., [47]). Figure 7.2 shows the average daily sleep duration of 6,366 active duty service members assessed in 33 studies with data collected during military operations, during training and education, and during deployments and combat missions. Each data point represents the average daily sleep duration for each population in the corresponding study. From this diagram, the extent of sleep deprivation across all these environments and studies is evident. Most averages are below the 7-h sleep criterion for good health, while none exceeds the approximately 8-h criterion for full cognitive functioning [4].

Numerous factors affect sleep patterns in military operational environments. The predominant stressors include factors exogenous to the individual per se, that is, factors associated with the environment in which the service member is required to live and work. Service members have limited opportunities to sleep at their preferred time due to operational commitments [64–66, 68, 70, 71]. The problem of circadian misalignment is further exacerbated by artificial lighting conditions in work environments, by natural sunlight received at circadian inappropriate times, and by shiftwork [5, 35, 49, 54, 60].

Shiftwork is a common practice in the military because almost all operational military units, especially when deployed, are required to function 24/7. The shift schedule that is selected depends on the organizational culture, the prior experience of the command leadership, and the availability of qualified personnel to stand watch. Depending on the shift (or in military parlance, “watch”) itself and other daily activities in which the individual and military unit are involved, a number of fixed and rotating watch systems are commonly used. Some of these schedules result in days that are other than 24 h in length. For example, the length of the day for an individual on a 5-h on watch and 10-h off watch (“5/10 or 5 and dime”) schedule can be considered either 15 or 30 h in length [65, 68]; the 5-h on/15-h off (“5/15”) schedule results in a 20-h day. Studies on naval vessels have revealed how some of these traditional watch schedules used at sea result in sleep deprivation, fragmented sleep, suboptimal performance, and worrisome levels of alertness [55, 59, 62]. It is noteworthy that the typical workday of active duty service members includes much more than just standing watch. Other duties and responsibilities may prolong the work day by 50% or more, with some crewmembers on US Navy ships working up to 15 h per day [30, 34, 44, 67].

The poor quality of sleeping conditions [45] leads to elevated levels of fatigue and affects morale as measured by self-reported mood states [14, 65, 68–70] and cognitive performance as measured by psychomotor vigilance tests. Studies conducted on multiple US Navy (USN) ships show the deleterious effect of sleep deprivation and circadian misalignment on psychomotor vigilance, with increased average reaction times and variability [14, 62, 64–66, 68–70]. The need to remain awake for long periods of time while deprived of sleep leads service members to consume large amounts of caffeinated beverages – to include energy drinks [63]. When taken in large quantities, caffeine affects sleep, making it difficult to fall asleep when opportunities are present [63, 74]. Even when there are opportunities to sleep, service members often have to sleep in berthing compartments which may not be optimal for good sleep. For example, our studies on USN ships have shown that noise from within or outside the berthing compartment, temperature conditions (both too hot or too cold), light, and environmental motion are some of the factors reported as disturbing sleep [62, 68, 70].

These sleep-disrupting factors can be classified as first-order effects in the sense that the existence of the stressors constitutes the cause of sleep pattern disruption. Combined with stressful life events, being away from home for extended periods of time, and combat exposure, military service members experience increased levels of occupational stress [31]. This second-order effect often results in further diminishment of sleep [41, 68]. It is no surprise that exposure to the often harsh military environment and living conditions affects the overall health of military personnel. Post-traumatic stress disorder (PTSD), depression, anxiety, and sleep disorders are the most common psychological and neurological injuries among service members [53].

An additional comment is appropriate regarding the “superhuman” appearance attributed to many military service members – also called the “myth of the warrior ” Shay [72]. Especially in operationally critical and dangerous conditions, adopting this attitude may be beneficial to members of the military profession, allowing them to accomplish their mission in the face of serious adversity. However, this same characteristic can become a problem when active duty military personnel deny their own need for sleep and replenishment. Research has shown that individuals who are sleep-deprived commonly fail to accurately assess their own level of sleepiness [27, 37]; they are largely unaware of their increasing cognitive deficits [77]. Therefore, sleep-deprived individuals may overestimate their ability to overcome the detrimental effects of sleepiness. Silimarly, when forced to perform while fatigued, military members are often inaccurate judges of their own limitations. This problem is further exacerbated by the widespread belief among service members that motivation may be the answer to overcoming tiredness, despite research findings demonstrating that motivation can only partially compensate for changes in performance due to sleep deprivation [56].

Overall, numerous factors contribute to poor sleep in the military operational environment. The diagram in Fig. 7.3 shows these factors clustered into three categories: psychological/pathological, environmental, and organizational.

Historically, the need to remain alert and the need to sleep whenever opportunities present themselves have been approached using pharmacologic and non-pharmacologic countermeasures and interventions. The optimization of performance through the implementation of best practices to retain/restore alertness, however, begins well before the actual operations commence. First, service members should be made aware of their biological need for sleep and how sleep deprivation affects them. Second, before operations begin, service members should be allowed, whenever possible, to bank sleep, i.e., to accrue sleep “in excess” as a reserve [6, 58]. To the extent possible, mission planners should take into account human alertness by using existing sleep and performance models to predict best and worst periods of performance [38], allowing planners to weigh risks and optimize shiftwork.

During operations , commanding officers should implement a sleep schedule for their unit. Even though long periods of sleep are not possible in the operational environment, “prophylactic naps” have been demonstrated to increase alertness [29]. The habitability of sleeping spaces should also be considered as a way to improve sleep, and enhanced lighting conditions may improve the alertness of sleep-deprived service members [20]. Because of the importance of having alert warfighters/service members, military organizations and law enforcement agencies have issued regulations and guidelines regarding fatigue management (e.g., [22]). In conjunction with these approaches, pharmacologic interventions may also be beneficial when appropriately implemented in the field to enhance performance by improving alertness [79] or to facilitate getting sleep when needed [15]. The pharmacologic and non-pharmacologic approaches to improve alertness and help service members sleep when needed are shown in the Fig. 7.4.

The military operational environment is notorious for its unpredictable nature. Service members are often challenged by irregular, or in some cases, unforeseen, operational duties, and long work hours. It is not surprising that active duty service members are chronically fatigued because they cannot get as much sleep as they need due to operational commitments and erratic schedules. These problems are further exacerbated by an increase in operational tempo (OPTEMPO), i.e., the pace of military operations, which has been excessive over the past two decades [21]. Service members not only have limited opportunities to sleep due to operational commitments, but they also find it difficult to sleep when they have spare time because their sleep opportunities often occur during circadian-misaligned time periods. They also experience chronic circadian desynchrony and low quality of sleep-related habitability factors in their sleeping compartments. Sleep, however, remains a critical requirement for humans. Performance and health are both affected by insufficient sleep . Long-term effects include insomnia and circadian scarring , which are common “hidden wounds” in military veterans. The military, like other organizations that require shiftwork, needs to embrace the importance of sleep health [17] and implement sleep hygiene practices as an inexpensive approach to optimizing operational performance, increasing personnel retention, and minimizing long-term health costs both for active duty service members and veterans.