Once the Free Navy's gate-commanding artillery, the rail guns are disabled when Bobbie destroys a reactor and knocks their structural bands loose from Ring Station.
The Medina rail guns are massive magnetic turrets mounted on the structural bands around Ring Station, the alien sphere at the slow zone's center. Built with Laconian-supplied materials and powerful fusion support, they allow the Free Navy to fire across the Ring approaches and make Medina's claimed control of the gates physically real.
During the coalition's assault, they destroy most of the Giambattista's incoming swarm, the decoy that keeps their attention fixed away from the smaller force landing at their bases. They prove fully capable of tearing apart craft, torpedoes, and rams until Bobbie Draper finds herself stopped by the guarded emplacements.
Bobbie uses a sacrificial landing boat to ram the reactor beneath a hotter gun while launching a rocket at its bunker. The blast shuts the gun down and causes the metal bands holding the artillery to pull away from the blue alien surface. The remaining guns cannot continue firing, and their defenders withdraw. The coalition has not captured a usable weapons system, but it has removed the Free Navy's ability to use it before the Roci enters the slow zone.
Huge hexagonal-base rail-gun turrets with fusion support, magnetic rails, vapor-assisted muzzles, and massive metal-and-ceramic bands clamped around an eerie blue alien sphere.
The rail guns are the gate fortress's decisive weapons, now disabled at the moment their control was meant to decide the battle.