Addressing the critical vulnerability of standard cellular networks during subterranean catastrophes, DARK5G introduces a resilient communication architecture designed to withstand infrastructure failure. Unlike conventional Over-the-Air(OTA) 5G, this system leverages robust leaky cable technology to maintain wideband connectivity and structural integrity even during tunnel collapses or widespread power outages. The solution features a rapid-deployment mobile core capable of achieving full operational status within 5 minutes, simultaneously restoring public communication and providing first responders with real-time situational awareness. Developed by Rinicom Ltd and i46 s.r.o. with funding from the Horizon Europe FIDAL program, and validated within the London Underground, DARK5G establishes a new standard for emergency response in complex underground environments.