Three Hours On, Nine Off: A Destroyer Tests Its Watch Schedule
Naval Postgraduate School researchers compared 3/9, 6/6 and 5/10 Navy watch schedules with wrist sensors. What they found, and how far it travels.
In this article11 sections
A destroyer on a 3/9 watchbill splits its watchstanders into four sections, and each section stands two three-hour watches a day. At 03:40, the section on the 03:00 to 06:00 watch is forty minutes in. It will stand that watch again at 15:00 today and at 03:00 tomorrow, so its sleep windows, 06:00 to 15:00 and 18:00 to 03:00, sit at the same clock times every day. On the older five and dime bill, that section would have been on the bridge at 03:40 only some of the time, and the rest of the week it would have been asleep, just woken, or trying to sleep through a noon that felt like midnight.
In the comparisons run at sea, the 3/9 came out ahead: three hours on watch, nine hours off, at the same clock times every day. On USS Jason Dunham in 2012, 3/9 crewmembers averaged 6.46 hours of sleep a day against 5.89 for the 6/6, and against the older 5/10 “five and dime” the 3/9 gave about the same total sleep (close to seven hours) but better sleep quality, mood and reaction time.
That difference, a fixed clock versus a drifting one, is what Dr. Nita Lewis Shattuck and Dr. Panagiotis Matsangas of the Naval Postgraduate School (NPS) in Monterey, California, spent more than a decade measuring on working ships. This piece goes through what they compared, how the schedules differ hour by hour, and where the evidence is thinner than the Navy’s enthusiasm suggests.
How do the three watch schedules differ hour by hour?
Three schedules appear again and again in the NPS work, and they differ in how many sections the crew is split into and how long the cycle takes to repeat.
| Schedule | Sections | Cycle | What the clock looks like |
|---|---|---|---|
| 5/10 (“five and dime”) | 3 | 15 hours | Watch times shift every day and repeat over a multi-day pattern |
| 6/6 | 2 | 12 hours | Same two six-hour watches every day |
| 3/9 | 4 | 12 hours | Same two three-hour watches every day |
The 3/9 and 6/6 rows follow from simple arithmetic. A 12-hour cycle fits into a day exactly twice, so the same section stands the same two watches daily. A 15-hour cycle does not fit into 24 hours, which is the whole problem. The five and dime amounts to a 15-hour day imposed on a 24-hour body, and within its three-day cycle sleep lands at a different clock time each day (Shattuck and Matsangas, Ergonomics, 2016).
The workload also differs. Under the 6/6, half the crew is on watch for a total of twelve hours out of every twenty-four. Under the 3/9, each person stands six. The price is more handoffs, and the NPS authors argue that shorter watches and steadier sleep more than pay for them, in sharper attention and a more predictable day.
What happened on USS Jason Dunham?
Jason Dunham (DDG-109) was operating in the Persian Gulf region in 2012 when the NPS team came aboard to interview crewmembers and monitor their sleep patterns, activity periods and reaction times. Sailors on the 3/9 were compared with sailors on the 6/6.
Volunteers wore an actigraph, a wristwatch-style motion sensor that estimates sleep and wake from movement. They also took the psychomotor vigilance task (PVT), a short reaction-time test in which the wearer presses a button as soon as a stimulus appears. PVT is a standard fatigue probe because lapses in it track sleep loss, and a wrist device can repeat it at set intervals over days.
Shattuck and Matsangas published the comparison in the proceedings of the Human Factors and Ergonomics Society annual meeting in 2016, under the title “Comparison of the 3/9 and 6/6 Watchstanding Schedules for Crewmembers of a U.S. Navy Destroyer.” The headline result is the sleep gap, 6.46 hours on the 3/9 and 5.89 hours on the 6/6. Press coverage of the work reported that the study came out in favor of the 3/9, though sailors had mixed reactions to living on it.
What did the same researchers find against the five and dime?
The 5/10 was the Navy’s default. NPS also compared it with the 3/9 in the nuclear reactor department of the carrier USS Nimitz in 2014, where crewmembers stood watch on the 5/10 for 17 days in June and, in November, on the 3/9 for 11 days (Shattuck and Matsangas, Naval Postgraduate School). The same department’s 5/10 results appeared in Ergonomics, among 77 crewmembers, tracking sleep patterns, mood and PVT performance. Together they are the nearest thing to a head-to-head in this literature, and the surprise is in the sleep totals: sailors on both schedules averaged close to seven hours a day. The 3/9 won on how that sleep was arranged. Reports of the comparison describe fewer sailors saying they lacked time to sleep on the 3/9 (52 percent, against 88 percent on the 5/10), reaction times roughly 30 percent faster and 40 to 50 percent fewer errors. The two schedules were run five months apart with different mixes of crew (69 people on the 5/10, 115 on the 3/9), so it is a comparison between groups, not within one.
Seven hours is the catch in the Nimitz result. If total sleep is the same, why does the Navy care? The answer points to timing. A sailor who gets four hours, stays up 20, and then sleeps at a time that does not match the body’s clock is in a different state from one who gets seven hours in the same place every day, even when the daily average matches. The averages hide the structure.
Being woken for a watch changes the picture
Most Navy fatigue discussion concerns the watch itself. The same schedules also decide how a sailor gets woken. On a 3/9, the person stands the 03:00 watch every day, so the messenger or shipmate who wakes them turns up at the same clock time daily, and sleep can be arranged around that known pickup. On a five and dime, the wake-up time moves by about nine hours a day, which means every watch begins with an interruption the body did not expect.
This is an inference from the schedule structure and from the sleep-inertia literature (see the explainer on grogginess right after waking). The NPS studies measured sleep, PVT and mood, and wake-up grogginess was not among them.
Fixed timing also solved a problem older than the destroyer. The U.S. Navy’s 18-hour submarine day had the same flaw in sharper form, a cycle that never matched the planet. The surface fleet’s five and dime was a milder version of that idea.
A single destroyer is thin evidence
Jason Dunham is one ship, and the 6/6 group was small: 41 sailors stood the 3/9 and 11 the 6/6, 52 in all. Sailors were not randomly assigned to schedules: which section works which schedule, and who volunteers to wear an actigraph, may be shaped by rank, department and operational role. A difference of about half an hour in nightly sleep, in groups that size, is suggestive and not conclusive.
Operational context confounds everything. These crews were deployed, running drills and standing watch at the same time, in berthing compartments where noise, lights and shipmates’ schedules vary. Sleep gets cut by events no watchbill controls: a general-quarters call, a refueling, a late drill.
Whether the findings extend to a hospital ward, a call center or a household is less clear. Sailors are young, fit, living in a closed environment and typically unable to leave a schedule they dislike. The principle that a stable, 24-hour-aligned cycle lets sleep land in the same place each day fits wider circadian research, but the sleep numbers belong to those crews, on those ships, in those years.
The cleanest reading is narrower than the Navy’s advocacy and still useful. Of the schedules compared at sea, the 3/9 came out ahead of the 6/6 and the 5/10 on sleep arrangement and alertness, and the drifting clock of the 5/10 is the feature the research keeps returning to. Neither crew reached the Navy’s seven-hour floor (6.46 and 5.89 hours), and a schedule on paper does not shrink the drills and maintenance that land in off-watch hours.
What did the Navy adopt after 2017?
After the 2017 collisions of USS Fitzgerald and USS John S. McCain, reviews of the surface fleet found that many officers had stood watch during refuelings at sea, strait transits and port arrivals on little or no sleep. Vice Adm. Thomas Rowden, commander of Naval Surface Forces, issued a fatigue and endurance policy asking for at least seven hours of sleep in 24 and directed cruisers, destroyers and amphibious ships to put circadian watchbills and shipboard routines in place by December 20.
The schedule kept evolving afterward. NPS assessed a 3-3-3-15 rotation on USS Stockdale (DDG-106) in 2016, a pattern that keeps the 24-hour repeat of the 3/9 while changing how the six hours of watch are spaced. Whether crews slept more under these watchbills is a separate question that the studies above do not answer.
FAQ
Why does the 3/9 schedule need more watchstanders than the 6/6?
It splits the watch into four sections instead of two, so a ship needs four fully qualified teams at every watch station, one standing watch while three are off. Each person stands only six hours of watch a day instead of twelve, but ships short on qualified people can struggle to fill all four, and every extra turnover means another handoff briefing.
What sleep target does Navy guidance give surface-ship sailors?
The 2017 surface-fleet guidance asks for at least seven hours of sleep in 24, either as seven uninterrupted hours or as five uninterrupted hours plus a two-hour uninterrupted nap. Vice Adm. Thomas Rowden directed cruisers, destroyers and amphibious ships to adopt circadian watchbills and shipboard routines by December 20 of that year.
Can sleep regularity be measured for a watch schedule?
Yes. A 2025 paper in the Journal of Sleep Research by Guzzetti, Matsangas, Banks and Shattuck applied the Sleep Regularity Index to 218 sailors on different watchbills for about a week underway. The 5-hours-on, 15-hours-off watchbill scored lowest on regularity, even though daily sleep duration did not differ significantly between watchbills.
What is the 3-3-3-15 schedule?
Crewmembers on USS Stockdale (DDG-106) tried a rotation of three hours on, three off, three on and fifteen off between March and September 2016, assessed by Matsangas and Shattuck in 2018. The numbers add up to 24, so the pattern repeats at the same clock times every day, and it asks a sailor to stand six hours of watch inside a nine-hour span.