Coast Guard Data Network Plus

From GovITwiki

Commonly known as CGDN+, this network is used to transmit information such as maritime-related law enforcement information and intelligence supporting drug interdiction, maritime safety and security data, vessel tracking data, search and rescue data, environmental hazard data, border control data, and emergency sealift management data.

(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.