“If modestly sophisticated countermeasures are anticipated for the IRBM (intermediate-range ballistic missile threat), then the European PAA will need to include multiple X-band radar and long-range IR (infrared) sensors that can provide concurrent data on IRBM trajectories similar to the countermeasures proposed for U.S. national missile defense,” the report states.

However, the report contends, “Phase IV of the European PAA may not be the best way to improve U.S. homeland defense. The speed of the Phase IV interceptor will need to be greater than can be achieved with a 21-in. missile to avoid being overflown by lofted ICBM trajectories from Iran if the interceptor is based in northern Europe (Poland).”