Germany's national rail network ground to a halt late on Tuesday night after a scheduled attempt to replace an ageing component in the railway's digital radio communication system triggered a cascade failure, stranding hundreds of thousands of passengers across the country. The outage, which initially raised fears of a cyber-attack, was traced to a fault in the GSM-R system — a 1990s-era 2G mobile technology that train drivers and traffic controllers rely on to communicate. Without it, no train is legally permitted to operate at full speed, and services were halted as a precaution, leaving passengers stuck on tracks between stations or waiting on platforms with little information about what was happening.

The backup system, which uses a separate mobile network provided by Deutsche Telekom, also failed — with SIM cards in onboard computers unable to be reliably identified by the network. In limited cases, trains moved at a cautious 30 kilometres per hour under visual-only conditions. A system reset was carried out within roughly 90 minutes, but untangling the resulting chaos across Europe's largest and busiest rail network — which carries around 50,000 trains a day across 33,400 kilometres of track — took considerably longer. Deutsche Bahn (DB), the state-owned company that operates the network, issued an apology on Wednesday.