Tensions with Iran are once again high, making plain the risk of unexpected conflict between Iran and the United States. In the event of such a conflict, the United States would likely rely heavily on regional missile defense architectures like the European Phased Adaptive Approach, or EPAA, designed to protect NATO from ballistic missile attacks from the Middle East. Yet the EPAA is fragile, with a single point of failure that a sensible adversary like Iran could exploit. Fortunately, there are practical steps that NATO and the United States can take to make EPAA more durable.

Single point of failure

At the heart of the EPAA are two Aegis Ashore sites in Romania (operational) and Poland (under construction). These sites are supported by four Aegis BMD destroyers and a forward-based TPY-2 radar in Turkey. With its high resolution and forward position, the TPY-2 is particularly useful for tracking a missile’s trajectory early in its flight. In the case of EPAA, this data is relayed from the TPY-2 in Turkey to the Aegis Ashore sites, which use it to guide their interceptors.

This tactic is called “engage on remote,” or EOR, allowing Aegis Ashore sites to provide BMD coverage for nearly all of NATO Europe. EOR enables a vastly greater defended area by allowing a shooter to launch an interceptor much earlier than if it had to wait for its own collocated radar to pick up the target. To put it simply: The earlier you fire, the more turf you can protect.

If the forward-based TPY-2 radar failed for any reason, the defended area of the two Aegis Ashore sites would shrink dramatically. The SPY-1 radars installed at the Aegis Ashore sites are too limited in range to enable defensive coverage of Europe on their own. Most military bases and major cities across Europe would become undefended. This makes the EPAA’s TPY-2 a single point of failure, one that a determined and imaginative adversary like Iran might exploit. Current events suggest the Iranians are attuned to this vulnerability: Iran has aided Houthi fighters in Yemen to target Saudi Patriot radars with UAVs, and have used UAVs in concert with ballistic missile attacks.

Given these challenges, achieving an effective defense of NATO will likely require a more layered and resilient sensor network than the current EPAA plan articulates.

Shoring up the EPAA

The fragility of the EPAA’s sensor network is not from lack of foresight. Rather, it stems from a failure to implement the policy as originally planned. When first announced, the EPAA included two additional sensor systems: the space-based Precision Tracking and Surveillance System (PTSS), and the Airborne Infrared program (ABIR). Such systems would have made EPAA much more resilient. The U.S. government canceled PTSS in 2013. ABIR also lost funding in the 2013 defense budget. The United States has not totally lost sight of these technologies, and research on space and air-based sensors has continued. Following through on elevated sensors would not only benefit EPAA in powerful ways but would enhance U.S. missile defenses globally.

In the nearer term, there are several other options that could improve the EPAA’s sensor architecture. One such option is to further integrate allied ship-based radars into NATO’s BMD architecture. Denmark, Germany and the Netherlands together have 10 ships with radars that could be modified for long-range BMD tracking. While integrating these systems may not provide a direct replacement to the TPY-2’s high-resolution imagery or geographic advantages, they could nevertheless add redundancy and help shore up sensor gaps. A second option could be to construct additional long-range, ground-based radars in and around the Mediterranean for persistent, redundant sensor coverage.

Another approach would be to upgrade the Aegis Ashore sites themselves with more advanced, longer-range radars. The SPY-1, although much evolved, is still based on 1980s hardware. Integrating newer technologies, such as active electronically scanned arrays that use gallium nitride, could improve range and sensitivity. Next-generation digital radars capable of operating in different bandwidths may offer further capability. Equipping Aegis Ashore with better sensors could enable it to maintain coverage even in the event of EOR failure.

The enemy gets a vote

In 1958, Cold War strategist Albert Wohlstetter wrote that U.S. confidence in its nuclear deterrent was based on “ignoring the full range of sensible enemy plans.” This same critical judgment should be applied to confidence in the EPAA as currently configured. Adversaries which rely heavily upon missile forces — like Iran — are likely to target the EPAA’s vulnerabilities. A more robust sensor architecture is necessary to prepare NATO’s defenses for these contingencies, improving U.S. and NATO preparedness for an unexpected Middle East conflict.