The ACDS upgrade is divided into two phases designated as Block 0 and Block 1. The Block 0 system replaces obsolete Naval Tactical Data System (NTDS) computers and display consoles with modern equipment and incorporates both new and upgraded NTDS software. Block 1 operates with the equipment provided under ACDS Block 0 but implements significant improvements in software capability. The Block 1 upgrade includes modifiable doctrine, the Joint Tactical Information Distribution System (JTIDS) for joint and allied interoperability, increased range and track capability, multi-source identification, National Geospatial-Intelligence Agency (NGA) based digital maps, and an embedded training capability.