BACKGROUND: Sleep deprivation is known to be a common problem in the U.S. Navy and has been documented using wrist-worn actigraphy in various operational studies that typically span 2 to 4 wk in duration. However, sleep patterns over an extended period of time have not been objectively measured.CASE REPORT: This 6-mo study used actigraphy and the Fatigue Avoidance Scheduling Tool (FAST) to quantify the sleep patterns of a 39-yr-old Commanding Officer (CO) of an Arleigh Burke class destroyer while the ship was forward-deployed. On average, the CO received 5.2 h of sleep daily and averaged 6 h time in bed each day. The participant received more than 8 h of sleep for only 2% (N = 3) of the study days; for 17% (N = 27) of the days, he received less than 4 h of daily sleep. For 15% of waking time, the CO had a predicted effectiveness of less than 70% on the FAST scale, equating to a blood alcohol equivalent of 0.08%—or legally drunk. The CO’s predicted effectiveness was below 65% approximately 10% of waking time.DISCUSSION: Results from this study are aligned with earlier research showing that crewmembers on U.S. Navy ships suffer from chronic sleep restriction. During a typical deployment, personnel accrue a considerable sleep debt even during normal operations. Should critical events with additional sleep restriction occur, the ship has limited reserve capacity, potentially placing her crew and their mission in grave jeopardy.Shattuck NL, Matsangas P. A 6-month assessment of sleep during naval deployment: a case study of a commanding officer. Aerosp Med Hum Perform. 2015; 86(5):481–485.