USNO NTP Network Time Servers

The Naval Observatory operates an ensemble of stratum 1 NTP servers which are synchronized to the USNO Master Clocks or to GPS as their stratum 0 reference clocks.

Network Time Protocol (NTP) is an Internet standard protocol which enables client computers to maintain system time synchronization to the US Naval Observatory Master Clocks in Washington, DC and Colorado Springs, CO.

NTP runs as a client program on a computer. It sends periodic time requests to one or more servers, obtaining server time stamps and using them to adjust the client's clock.

Typical accuracy achieved is in the range 1 - 30 ms continuous, and is highly dependent on the symmetry and speed of the Internet path between client and server. Best results are achieved using a combination of servers which are closest to the client in a network sense.

To obtain precise time from USNO NTP servers, follow these procedures:

  1. Download NTP client software from ntp.org.
  2. Select several NTP servers and add to your client configuration.
  3. Run the NTP client on your machine.

We request that you allow no more than three of your clients to poll our servers directly. Organizations with many clients should obtain time from local stratum 2 servers. ISPs should configure routers or firewalls to serve as stratum 2 servers to the ISP network. Dialin clients should contact your ISP for information about NTP services.

All of the following stratum 1 NTP servers are open to stratum 2 servers within the same time zone and to others by arrangement. Individual users should consult the public list of stratum 2 servers.

Please note that these servers support only Network Time Protocol (IETF RFC-1305/ RFC-5905) and Simple Network Time Protocol (SNTP).

WE STRONGLY RECOMMEND THAT YOU CHOOSE ONE OR MORE SERVERS CLOSE TO YOU, AND IN ADDITION SELECT OTHER SERVERS FOR REDUNDANCY.


Recent NTP Files

  • NTP Leap-seconds file
  • NTP Stable release


  • U.S. Eastern Time Zone

  • tick.usno.navy.mil
  • Location: Time Service Dept., U.S. Naval Observatory, Washington, DC
    Synchronization: NTP V4 primary (USNO Master Clock H-masers)
    Access Policy: open access for MIL, GOV, and other stratum 2 servers.

  • tock.usno.navy.mil
  • Location: Time Service Dept., U.S. Naval Observatory, Washington, DC
    Synchronization: NTP V4 primary (USNO Master Clock H-masers)
    Access Policy: open access for MIL, GOV, and other stratum 2 servers.

  • ntp2.usno.navy.mil
  • Location: Time Service Dept., U.S. Naval Observatory, Washington, DC
    Synchronization: NTP V4 primary (USNO Master Clock H-masers)
    Access Policy: open access for MIL, GOV, and other stratum 2 servers.

    U.S. Mountain Time Zone

  • tick.usnogps.navy.mil
  • Location: US Naval Observatory Alternate Master Clock, Colorado Springs, CO
    Synchronization: NTP V4 primary (USNO Master Clock H-masers)
    Access Policy: open access for MIL, GOV, and stratum 2 servers

  • tock.usnogps.navy.mil
  • Location: US Naval Observatory Alternate Master Clock, Colorado Springs, CO
    Synchronization: NTP V4 primary (USNO Master Clock H-masers)
    Access Policy: open access for MIL, GOV, and stratum 2 servers



    For further information contact
    Time Service Dept., USNO

    Back to Time Service Home Page
    "The inaudible and noiseless foot of Time." --W. S.