A brutal Dominion War engagement over a small planet's communications relay.
AR-558 is a planet in Dominion territory where Starfleet captured a Dominion communications relay array during the war. In the Deep Space Nine episode The Siege of AR-558, the Defiant delivers supplies to the Starfleet troops who have been holding it against Jem'Hadar attacks for five months, far longer than their planned rotation.
The defenders are exhausted and battle-weary, and the area is seeded with cloaked mines called houdinis. Captain Sisko, Dr. Bashir, Ezri Dax, Nog and Quark stay to help when the Jem'Hadar prepare a major attack. Nog is shot during a scouting mission and loses his leg.
The outnumbered defenders hold off the final assault and keep the array, though at heavy cost. Nog's injury and recovery are followed in It's Only a Paper Moon, where he takes refuge in Vic Fontaine's holographic lounge. The episode is remembered as one of Deep Space Nine's grimmest portraits of war.