Next-Generation operational control segment (OCX) In 2010, the United States Air Force announced plans to develop a modern control segment, a critical part of the GPS modernization initiative. OCS will continue to serve as the ground control system of record until the new system, Next Generation GPS Operational Control System (OCX), is fully developed and functional. OCX features are being delivered to the United States Air Force in three separate phases, known as "blocks". The OCX blocks are numbered zero through two. With each block delivered, OCX gains additional functionality. In June 2016, the U.S. Air Force formally notified Congress the OCX program's projected program costs had risen above US$4.25 billion, thus exceeding baseline cost estimates of US$3.4 billion by 25%, also known as a critical Nunn-McCurdy breach. Factors leading to the breach include "inadequate systems engineering at program inception", and "the complexity of cybersecurity requirements on OCX". In October 2016, the Department of Defense formally certified the program, a necessary step to allow development to continue after a critical breach. In July 2021, all OCX monitor station installations had been completed. OCX monitoring stations are expected to transition to operations in "early 2023," and the U.S. Space Force hopes to complete operational acceptance for all of OCX in 2027. OCX Block 0 (launch and checkout for Block III) OCX Block 0 provides the minimum subset of full OCX capabilities necessary to support launch and early on-orbit spacecraft bus checkout on GPS III space vehicles. Block 0 completed two cybersecurity testing events in April and May 2018 with no new vulnerabilities found. In June 2018, Block 0 had its third successful integrated launch rehearsal with GPS III. The U.S. Air Force accepted the delivery of OCX Block 0 in November 2017, and is used it to prepare for the first GPS launch in December 2018. OCX Block 1 (civilian GPS III features) OCX Block 1 is an upgrade to OCX Block 0, at which time the OCX system achieves Initial Operating Capability (IOC). Once Block 1 is deployed, OCX will for the first time be able to command and control both Block II and Block III GPS satellites, as well as support the ability to begin broadcasting the civilian L1C signal. In November 2016, the GAO reported that OCX Block 1 had become the primary cause for delay in activating the GPS III PNT mission. Block 1 completed the final