A 1979 briefing note on the National Intelligence Estimate (NIE) of the missile gap concluded that the NIE's record on estimating the Soviet missile force in the 1970s was mixed. The NIE estimates for initial operational capability (IOC) date for MIRVed ICBMs and SLBMs were generally accurate, as were the NIE predictions on the development of Soviet strategic air defenses. However, the NIE predictions also overestimated the scope of infrastructure upgrades in the Soviet system and underestimated the speed of Soviet improvement in accuracy and proliferation of re-entry vehicles.