 IBM was at that time starting work on the Semi-Automatic Ground Environment (SAGE) system for the US Air Force, which had a large number of features in common with a booking system; remote communications with "offices", real-time updating, interactive user terminals, and storage of large amounts of information.Low-level exploratory work continued for some time before IBM was able to offer a formal development contract on 18 September 1957.Development of the Sabre system started, which many computer historians have suggested was one of the major milestones in the commercialization of computers.