The core of Israel's active defense plan remains the Arrow antiballistic missile program. Test results of the Arrow have been promising. They indicate not only the mutual benefits of close cooperation between Washington and Jerusalem, but also the technical promise of Israel's missile defense system.
But serious decisions must still be made. Faced with a steadily nuclearizing Iran, Israel must consider whether it can rely entirely upon a suitable combination of deterrence and active defenses or whether it must also prepare for preemption. The results of this essential consideration will have existential consequences for the Jewish state.
Israel's preemption option should now appear less urgent. If the Arrow were truly efficient, even an irrational Iranian adversary armed with nuclear and/or biological weapons could be dealt with effectively. If Israel's nuclear deterrent were immobilized by an enemy state willing to risk a massive "counter-value" Israeli reprisal, that aggressor's ensuing first strike could still be blocked by Arrow. So why even consider preemption against Iran?
The answer lies in certain crucial assumptions. "Operational reliability of intercept" is a "soft" concept, and any missile defense system will always have "leakage" – it can't stop every incoming missile. Whether such leakage would fall within acceptable levels must ultimately depend, primarily, upon the kinds of warheads fitted upon the enemy's incoming missiles. Shall Israel now bet its very life on a capacity to fully anticipate offensive enemy capabilities? We think not.
A tiny number of enemy missiles penetrating Arrow defenses could still be "acceptable" if their warheads contained only conventional high explosive or even chemical high explosive. But if the incoming warheads were nuclear and/or biological, even an extremely low rate of leakage would be intolerable. This means that Israel cannot depend upon its antiballistic missiles to defend against any future attack by Iran using a weapon of mass destruction. Even if Israel could expect a 100 percent reliability of interception for Arrow, this would do nothing to blunt the unconventional threat from terrorist surrogates. Special points of vulnerability for Israel would be Lebanon, with Hizbullah proxies acting for Iran, and Gaza, where Iran-supported Hamas is also developing dangerous ties with Al Qaeda.
Israel still faces certain state enemies whose undisguised preparations for attacking the Jewish state are genocidal, and who may not always be rational. Israel has every right to act preemptively when facing an existential assault. Known as "anticipatory self-defense," this general right is affirmed in both codified and customary international law, including the 1996 Advisory Opinion issued by the International Court of Justice.
Israel must continue to develop, test, and implement a missile interception capability. It must also prepare for certain possible preemptions, and enhance the credibility of its nuclear deterrent. Israel must operationalize a recognizable second-strike force, sufficiently hardened and dispersed, and ready to inflict a decisive retaliatory salvo against enemy cities.
Arrow is necessary for Israeli security, but it is not sufficient. To achieve a maximum level of security, Israel must also take appropriate and coordinated preparations for preemption and deterrence. Ballistic missile defense will do nothing to thwart terrorist surrogates of Iran who could utilize ordinary ships, cars, or trucks as nuclear-weapon delivery vehicles.
Left alone in its nuclear plan, Iran would probably share certain of its atomic munitions with assorted anti-Israeli proxies in Lebanon, Syria, Gaza, Pakistan, Saudi Arabia, and Iraq. Ballistic missile defense is indispensable for Israel, but it is also critical for both Jerusalem and Washington that Iran's nuclear infrastructures be destroyed at their source.
• Louis Rene Beres is a professor of international law at Purdue University. He is the author of many books and articles on nuclear strategy and nuclear war. Air Force Lt. Gen. Thomas McInerney (ret.), coauthor of "The Endgame: The Blueprint for Victory in the War on Terror," is chairman of the Iran Policy Committee Advisory Council.