The Battle of the Underdark was battle fought in the city of Erebus in the Nyxian Underdark, an underground cavern on the planet Nyx, between the Yellow Jackets and a combination of local police Special Response Teams, Interstellar Police officers, and corsairs under the command of condottieri Siegfried Metzger on the night of January 21st and into the early morning of January 22nd of 3285. The battle came off the heels of the Battle of the Seraphim Grand and was concurrent with several minor skirmishes throughout the Banat region. The battle began with a police raid on the Yellow Jackets headquarters on the planet, along with synchronised raids by corsairs on other Yellow Jacket safehouses in the city, and concluded with the terrorist bombing of the city. Several large stalactites on the roof of the cavern were disconnected via explosive charges, and several thousand tons of rock collapsed into the cityscape, destroying and damaging buildings and starting numerous fires. The thick smoke choked the cavern and hundreds of thousands of people died or were injured due to the blasts, fires, collapsing rock, and smoke inhalation.
The Yellow Jackets achieved a tactical victory in the battle, but the long-term consequences contributed to their ultimate demise. The Yellow Jackets were declared 'domestic terrorists' by the Central Galactic government and the Interstellar Police, Space Forces, and Marines were tasked with pursuing them with the full power of the armed forces of the Republic.
The Pirate War began in late November 3284 when a crew of Yellow Jackets operating illegally-armed spacecraft bombarded the Seraphim Grand Orbital Resort above the planet Keystone, killing several thousand people and initiating a widespread conflict between several space pirate gangs across the Outer Colonies, Banat, and Arcturus regions of interstellar space. The ensuing gang war comprised skirmishes throughout these areas, while the Space Forces attempted to maintain control of public security and the Interstellar Police launched a criminal investigation into the Yellow Jackets.
These efforts culminated in a combined police and corsair raid on Solomon Lazar's compound and on several Yellow Jacket safehouses on the planet Nyx in late January 3285. Nyx's subterranean capital city, the Underdark, was noted by media as a "wretched hive" where various gangs possessed undue influence over the political and economic situation of the city. The Yellow Jackets were often remarked to have many police officers and watchmen on their payroll. Sufficient evidence was gathered to implicate Solomon Lazar as the supreme chieftain of the Yellow Jackets, and his involvement or knowledge of the gang's violent and criminal activities, including decades-long human trafficking networks, heist and theft operations, assassinations, and bombings, as well as his control of police corruption in the Underdark. The raid was planned by two Interstellar Police officers now identified as members of the illustrious Silver Team, and launched on the night of January 21st.
A group of four Special Response Teams comprising ten SRT officers each were assembled at the Metro-Dark Police Vehicle Depot at 2300 Nyxian Mean Time. A battalion of corsairs under the command of Siegfried Metzger assembled there as well. Three teams departed in transport helicopters to Lazar's compound along with Metzger himself and the two ISPC officers. The remaining team divided into pairs and directed each a platoon of corsairs in assaulting three known Yellow Jacket safehouses in the city. A coordinated, synchronised raid on these locations began at 2400 NMT. Police snipers engaged the guards outside the compound before the three teams launched the assault at the side windows and front entrance of the compound, a manor house built into the rock of an enormous stalagmite.
Three SRT officers were killed during the initial assault, but at least ten Yellow Jacket enforcers were killed as well. Three Yellow Jacket enforcers were injured and evacuated. Ten police officers were injured and evacuated as well. During the raid, Lazar slipped away via an escape tunnel and sped away in an aerodyne hovercraft. As a police helicopter gave chase, the aerodyne reportedly fired antiair missiles and downed the police vehicle. Several corsairs boarded the police helicopter with Metzger and they pursued the escaping Lazar while the remaining officers secured the compound.
At the same time, the corsairs and SRT officers launched their raids on the Yellow Jacket safehouses, resulting in the deaths of three further officers and four wounded. Dozens of Yellow Jacket gangsters were killed or injured during these raids.
The helicopter carrying Metzger and three companion mercenaries, as well as a riding animal, pursued Lazar's aerodyne through the Underdark and up to the planet's surface. There, hazy fog and corrosive air prevented easy identification or tracking of the hovercraft. By the time they reached the escapees at the Metro Spaceport, the Yellow Jackets were quick-launching a rocket craft to escape into orbit. Metzger allegedly seized control of the helicopter and recklessly climbed in altitude, whereupon he lost control of the aircraft. It plummeted to the ground and crashed, injuring most of the occupants and killing the pilot. One of the mercenaries died of wounds en route to the Metro Hospital.