DHS Core Network

From GovITwiki

Also known as the DCN, this network is used to transmit sensitive but unclassified data related to DHS’s homeland security mission in areas such as customs and border patrol, intelligence and warning, and domestic counter-terrorism.

(Description comes from from General Accounting Office document GAO-07-455)

The GovITwiki Intelligence Agencies page lists the U.S. government's major secret and sensative but Unclassified networks.