Phase 4, Original Planned Deployment Date: 2020 (Cancelled)

• 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.

• 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.

• Space-based sensors would have likely played an increasingly important role in Phase 4.