The 2001B-1 part of the Litton navigation systems was the first major navigation system upgrade in the 21st century. It provided the most up-to-date navigation, navigation guidance, and navigation maintenance available for the Litton navigation system. The 2001B-1 part of the navigation package included software that worked with the ground systems and a real-time, three-dimensional geographic information system (GIS) map. This allowed a greater degree of situational awareness and management of the navigation system. Additionally, the 2001B-1 part of the system included new digital terrain elevation data, Iridium satellite navigation systems, and the Air-Grid system. These features allowed a significant improvement in the overall accuracy and functionality of the Litton navigation system.