EPAA Phase 4

Phase 4, Original Planned Deployment Date: 2020 (Cancelled)
Missile Platforms and Numbers	The platforms supporting the SM-3 interceptors under Phase 4 would have remained the same as those deployed under Phase 3 – sea-based platforms and the “Aegis-Ashore” deployments in Romania and Poland.
SM-3 Variant and Numbers	The SM-3 Block IIB would be deployed; planned numbers unknown. It was planned to have had an improved seeker and a higher performance booster, with a velocity of 5-5.5 km/sec. This was expected to marginally improve the Block IIA’s “limited” capability to counter ICBMs. According to the Defense Science Board (2011), the SM-3 IIB’s planned mission to intercept targets prior to the deployment of multiple warheads or penetration aids – known as “early intercept” – required “Herculean effort and was not realistically achievable, even under the most optimistic set of deployment, sensor capability, and missile technology assumptions.”. In FY2011, the United States awarded three concept definition / planning contracts for the Block IIB.
Sensors and Combat Systems	Space-based sensors would have likely played an increasingly important role in Phase 4.