The SEA 1439 Phase 4A Replacement Combat System (RCS) project was established to provide each of the Royal Australian Navy (RAN) COLLINS Class submarines with the United States (US) Navy (USN) Tactical Command and Control System, minor improvements to the combat system augmentation sonar, and shore facilities for integration, testing and training. Shore based systems are located at the Submarine Training and Support Centre at HMA Submarine STIRLING (WA) and a reference laboratory in the US at the Naval Undersea Warfare Centre. The project required the development of system commonality between the RAN and USN.