Defense Outpost 665 was a Federation outpost, an R1 Invictus-class defense outpost space station. In Starfleet service in the later 23rd century, around the 2280s decade, this defense station was located on the border of the Triangle.
On reference stardate 2/1704.05, a class from Star Fleet Academy participated in a weapons check on Defense Outpost 665, during which a cadet accidentally triggered an overload in one of the phaser banks. The resulting a chain-reaction explosion destroyed over half the station. (FASA RPG module: Regula-1 Orbital Station Deckplans)