The NSA began operating MAINWAY, a massive database system built to support the STELLARWIND surveillance program, collecting telephone metadata from major U.S. carriers including AT&T, Verizon, and T-Mobile. Built in urgent haste after September 11, MAINWAY became what sources described as 'the largest database ever assembled in the world,' ultimately containing over 1.9 trillion call-detail records (CDRs) including phone numbers of callers and recipients, call times, positions, and durations. The database ingested over one billion new records daily from telephone companies as part of the warrantless surveillance program. MAINWAY enabled NSA to create comprehensive 'contact chain' profiles on global citizens, mapping social networks and communication patterns without warrants or court oversight. The system operated alongside STELLARWIND's content collection, providing the infrastructure for unprecedented mass surveillance of American communications metadata. Private sector telecommunications partners began sending telephony and Internet metadata to NSA as early as November 2001, with the FBI commandeering records and NSA processing the information for intelligence analysis. This represented a fundamental shift from targeted surveillance to bulk collection, affecting millions of Americans' communications and establishing the foundation for modern mass surveillance capabilities.