June 24, 2025: The U.S. Navy is using $200 Oura fitness rings to monitor the health of sailors. The test subjects are 1,600 sailors serving aboard ships of the USS Ford carrier group. Those wearing the rings are volunteers. The rings enable Navy researchers to study factors such as how long and how well sailors sleep, along with other health indicators. The anonymous data is transmitted to Starlink satellites overhead and back to Navy researchers based in San Diego.

The origins of the Oura ring project date back to 2017, when the Navy suffered two ship collisions with civilian merchant ships. These incidents killed 17 Navy sailors. Collisions and accidents aboard ships continue to be attributed to fatigue. This led to the Command Readiness, Endurance, and Watchstanding (CREW) program, developed by the Naval Health Research Center. Sailors were first equipped with wearable monitoring devices in 2021. These devices, like the Oura rings, do not generate signals that could reveal the wearer’s or their ship’s position.

One problem was that this study initially had no official backing or budget. The study was started by officers in the Pacific Fleet and fleet staff, who sought official recognition and funding from the Department of Defense. The growing success of the health monitoring effort is expected to eventually secure recognition and budgets. However, official adoption risks introducing crippling bureaucracy and potential misuse of the data.

This is not the Navy’s first effort in this area. In 2014, the Navy completed a decade-long research effort, concluding that a half-century-old practice designed to keep sailors on nuclear submarines alert while monitoring nuclear reactors was flawed. In the 1960s, the Navy noted that sailors monitoring nuclear reactors on submarines became fatigued toward the end of their eight-hour shifts. As a result, the Navy adopted an 18-hour workday, with sailors required to monitor reactors for only six hours per shift. Despite this change, sailors still experienced fatigue. Since 2005, the Navy has been researching why. It turns out that a schedule out of sync with the 24-hour day was itself a source of fatigue because the human circadian rhythm is based on a 24-hour cycle, and there is no practical way to alter this.

Navy researchers also noted that commercial firms found workers who frequently changed shifts suffered from reduced alertness, productivity, and morale, all due to disruptions in the circadian rhythm. The circadian rhythm is most efficient when people sleep at night, though working regular night shifts long-term can be managed with some decrease in effectiveness. The greatest losses in alertness and efficiency occur when sleep schedules constantly change. Thus, the Navy’s traditional work schedule was highly inefficient.

The Navy tested a new submarine work schedule that respected the circadian rhythm and found, through sensors worn by sailors during testing, that alertness was significantly improved. Opinion surveys also showed much higher morale. Sailors tending reactors still experienced fatigue toward the end of their shifts, but not to the extent they did under the 18-hour day. The Navy implemented a 24-hour day for submarine crews, with sailors always working the same shift and sleeping on a regular schedule. The new schedule was greatly appreciated because it aligned with the circadian rhythm, and sailors quickly felt the beneficial impact.