Using archival materials obtained from the Port Authority of New York and New Jersey, we analyze networks of communication and interaction among responders to the World Trade Center disaster. Our findings indicate substantial variability in individual radio communication system usage, with both communication volume and number of partners exhibiting distributions with long upper tails. Responder communication patterns are well-described by a fairly simple four-role structure and exhibit substantial similarity across responder groups (both specialist and non-specialist). Occupancy of coordinating roles is influenced by formal institutional status, but the vast majority of hub role occupancy appears to be emergent in character. Examination of both radio transcripts and police reports suggests that much of the communication among WTC responders is centered on problems of spatial reasoning and peer location, possibly providing an explanation for the importance of improvised coordination at the event site. Although these problems appear to have posed substantial challenges for responders at Ground Zero, we find the global communication/interaction network among Port Authority officers to be fairly well-connected, with little evidence of large-scale fragmentation (despite perceptions to the contrary). Implications of these findings for the modeling of communication networks in emergency settings are discussed.