The Attack on the Nostril of Palpatine was an attempt by the Rebel Alliance to destroy the Nostril of Palpatine before the superwepaon could be deployed. The battle itself is still highly classified.
In 9 ABY, the Rebel Alliance learned of the existence of the Nostril of Palpatine, a potentially devastating superwepaon in the possession of renegade Imperial Warlord, Celie Namgadi. The weapon had only just been completed but was yet to see action; should it become active, it could tip the scales of the conflict against the Alliance.
To complicate matters, Celie's fleet, headed by the Super Star Destroyer Atom Smasher had recently begun raiding worlds around the Frood Sector, stretching the available resources thin. The Alliance were left in a situation where they could deal with the Eye or the renegade fleet, but not both.
Fortunately, information gathered from R. Jones, an agent of Namgadi's, revealed a key flaw in the Warlord's battle plan. The Nostril itself was virtually undefended, leaving it vulnerable to attack. The plan, code-named Operation Slimy Green called for a small force of fighters and ships to slip in and destroy the battlestation while the rest of Celie's fleet were otherwise occupied.
From the outset it became apparent that Warlord Namgadi had not thought through the defense of the Superweapon. Too slow and ungainly to move, it couldn't maneuver to escape the battle, nor was it fast or agile enough to bring its main weapon to bear. The stations two Beta-class ETR-3 escort transports were deployed to protect it, but at Celie's orders they were told to remain close to the Superweapon to defend it. As a result, the ships were not able to use their full speed and mobility, hampering their effectiveness.
The Trowzaar garrison scrambled their own TIE Fighters to support the force, but the ships were outnumbered by the Rebel Forces. The Rebel X-Wing fighters quickly engaged the fighters, while the Y-Wings of Glod Squadron attacked the two escorts, along with the Bacchus III. The first escort was crippled in moments, while the second managed to hold up under the assault.
Realising that by now Namgadi's fleet (and the Atom Smasher in particular) could be headed back, the Rebels turned their attention towards the Nostril itself. The X-Wings and Y-Wings began attacking the ship, only to find that its hull was too thick for their weapons; while they were slowly whittling it away, its hull remained intact. Even with the Bacchus III adding its firepower, the ship remained largely intact.
Fortunately, analysis of the ship revealed a fatal design flaw manifested itself; a poorly secured access hatch to the main reactor. After blowing open the panel, a lone badly-dressed X-Wing pilot was able to launch a Proton Torpedo into the ship's core. The weapon set off the reactor, which then exploded, destroying the entire ship and its crew.
Namgadi's fleet never returned to Trowzaar II; the Atom Smasher and all the other ships apparently vanished or joined up with a different Imperial faction. The destruction of the Nostril was the catalyst for the liberation of the Frood Sector. With Namgadi dead and her fleet missing, there was very little organised resistance to the Rebel forces; after decades of corruption and systematic exploitation, the people of the sector welcomed the Rebels.
For their part, the Rebels classified all the details of the battle as well as the schematics of the weapon.