Key to its defense was a huge queen.
Following the landing on Char, the combined Raynor's Raiders/Terran Dominion forces, under Commander Jim Raynor and General Horace Warfield, had to decide on a way to weaken the Zerg Swarm defenses before they made their final assault on the primary hive cluster.
Raynor decided to attack the nydus network. Warfield offered elite soldiers but Raynor refused, knowing he would need a tight squad. Warfield also requested that Raynor save several soldiers who fled into the network during the landing. Raynor, Findlay, Chief Engineer Rory Swann and scientist Egon Stetmann descended into the tunnels, fighting their way past hordes of zerg so they could plant seismic charges which would eventually flood the system with lava, destroying it. They were forced to destroy the giant queen, then flee as the lava rose.