A U.S. Submarine Day is 18 hours long, Not 24

At sea, a typical U.S. Navy submarine day is 18 hours long, not 24.

How Long is a Submarine Day?

At sea, a typical U.S. submarine day is 18 hours long, not 24. Crews are separated into 3 different watch sections with 6 hours on watch and 12 off. [1]

Why Does the Navy Use 18 Hour Days on a Submarine?

The 18-hour day is a matter of practicality; it allows submarines to be on watch 24/7 with the space limitations of the submarine taken into account.

A U.S. Submarine Day is 18 hours long, Not 24

A U.S. Submarine Day is 18 hours long, not 24

What Does Hours “Off” Mean?

A crew member’s  “off” time is the time they are off the watch. They do a number of things during this time including drills, maintenance, and sleep.

Has it Always Been an 18-Hour Day?

Since the 13th century, maritime workers around the world used a 4 hour on, 8 hours off schedule. [2][3]

The 18-hour day was created in the 1960’s to address the fact that in modern times submariners were suffering from sleep deprivation on long patrols due to the need to do things like train and conduct drills on their 8-hour off period. Scientists are showing that 18-hour workdays have a positive effect on submariners. [4]

This video can help you understand the history of submarines. Understanding the history of submarines helps understand why keeping an 18-hour schedule can make a difference over the duration of patrols.

How Do We Define “a Day”?

When we say submarine days are 18-hour days we aren’t referring to the definition of a day as 24 hours, we are referring to the definition of a day in a more broad sense and as a workday or schedule. We are referring to the way a day is experienced by a given group of people, rather than a day as a relation to the sun. [5]

The 18-hour day can also be referred to as a watch system or watch schedule.

Do Other Countries Use Different Watch Systems?

Other countries use different variations of the watch schedule to accomplish the same thing as the U.S. Navy’s 18-hour days. See a list of watch systems here.


U.S. Navy submarines use an 18-hour schedule, thus for all practical purposes a day is 18-hours long on a U.S. Navy submarine.


  1. Submarine Frequently Asked Questions. 22. What does the crew do during its free time?“. Navy.mil. Retrieved Feb 17, 2016.
  2. Why 18-hour schedule on submarines“. Ask.metafilter.com. Retrieved Feb 17, 2016.
  3. Studies could mean end of 18-hour days on subs“. Archive.Navytimes.com. Retrieved Oct 7, 2015.
  4. US Navy approves changes for submariners’ sleep schedules“. Foxnews.com. Retrieved Feb 17, 2016.
  5. day“. Dictionary.com. Retrieved Feb 17, 2016.
  6. Watch system“. Wikipedia.org. Retrieved Feb 17, 2016.

"A U.S. Submarine Day is 18 hours long, Not 24" is tagged with: Systems, Time, United States Armed Forces, United States of America

Vote Fact or Myth: "A U.S. Submarine Day is 18 hours long, Not 24"

Your Vote: {{ voteModel || 'no vote' | uppercase }}

btaylor on
Supports this as a Fact.

yes it helps people soooo FACT