Precise Time
The U. S. Naval Observatory is charged with maintaining the DoD reference for Precise Time and Time Interval (PTTI). That reference is UTC(USNO).
USNO Master Clock
The DoD common time reference is the U.S. Naval Observatory Master Clock. It is generated at USNO in Washington, D.C. and at the Alternate Master Clock Facility at Schriever AFB in Colorado.
GPS
USNO monitors the GPS constellation and provides system timing offsets to 2SOPS, timing data for individual GPS satellites, and time transfer services using GPS.
Computer Display Clocks
USNO servers provide a wide variety of web-based time synchronization products including embedded web clocks to display UTC(USNO) on other web pages.
TWSTT
The highest precision and accuracy in time dissemination is provided through Two-Way Satellite Time Transfer (TWSTT). USNO provides operational time transfer and calibration services for TWSTT.
Telephone Time
USNO provides both voice announcements of the time, and services to synchronize systems over telephone modems.
NTP
Network Time Protocol (NTP) is an Internet standard that enables client computers to synchronize to USNO. NTP runs as a client program on a computer.