The Use Case Trace (UCTRACE) is SAE publication AIR6519 of the Department of Defense Unmanned Control Segment (UCS) Architecture. This document is the SAE publication of the Department of Defense UAS Control Segment (UCS) Architecture: Use Case Trace (UCTRACE) Version 3.4(PR) approved for Distribution A public release 15.S-1859. This information is produced from a script run against the System Use Case Model contained in the UCS Architecture Model AS6518-MODEL.eap configuration item. The System Use Case Model includes@ at its lowest level of elaboration@ use cases Level 2/3 (L2/L3) that describe specific scenarios of message exchanges between Actors and internal system Participants via ServiceInterfaces. These message exchanges provide a way to create detailed traces that answer the question: ??What UCS service interfaces must my components implement to satisfy functional requirements represented by a given Level 2/3 UCS use case??? The AIR6519-UCTRACE spreadsheet contains trace information derived directly from the message sequences in the L2/L3 use cases.