Defense Data Network
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The Defense Data Network (DDN) was a separate instantiation of the ARPANET used by the United States Department of Defense from 1983-1995 for its Internet services.
The DDN began as the MILNET, a network formed in 1983 when military sites split off the public ARPANET. As a large-scale, private internet, the DDN provided Internet Protocol connectivity across the United States and to US military bases abroad. Throughout the 1980s it expanded as a set of four parallel military networks, each at a different security level. These networks transitioned to become the NIPRNET, SIPRNET, and JWICS networks in the 1990s.
The four DDN subnetworks were:
- Military Network (MILNET) for Unclassified traffic
- Defense Secure Network One (DSNET 1) for Secret traffic
- Defense Secure Network Two (DSNET 2) for Top Secret traffic
- Defense Secure Network Three (DSNET 3) for Top Secret/Sensitive Compartmented Information (TS/SCI)
MILNET and DSNET 1 were common user networks, much like the public Internet, but DSNET 2 was dedicated to supporting the Worldwide Military Command and Control System (WWMCCS) and DSNET 3 was dedicated to supporting the DOD Intelligence Information System (DODIIS).
