The Islamic Republic is in possession of the Middle East’s largest arsenal of missiles, most of which are of the short- and medium-range ballistic variety, and many of which could be equipped with a nuclear warhead. In addition, the Iranian proxy Hizballah has its own massive stockpile of rockets. As Michael Eisenstadt explains, missiles play a crucial role in Tehran’s strategic thinking, and pose a number of dangers:
[T]he recent nuclear accord with Iran . . . did not impose new constraints on Iran’s missile program. On the contrary, it loosened [existing ones]—and included provisions for their lifting in eight years, if not sooner. Iran’s missile force could double or triple in size by the time the major limits imposed [on its nuclear program] by the deal are lifted fifteen years from now. By then, Iran’s growing missile and cyberwarfare capabilities will pose major challenges to regional missile defenses, military and critical-infrastructure targets, and civilian population centers. This would make preventive action by Israel or the United States, in the event of an attempted Iranian nuclear breakout, much more costly.
[Furthermore], an Iranian nuclear missile force would be highly destabilizing. Short missile-flight times between Iran and Israel, the lack of reliable crisis-communication channels, and the impossibility of knowing whether incoming Iranian missiles are conventional or nuclear could someday spur Israel—and any other regional nuclear states that emerge in the interim—to adopt a launch-on-warning posture, undermining the prospects for a stable nuclear deterrent balance in the region.
[Already, Iran has established a “deterrence triad” that ] rests on its ability to: (1) threaten navigation through the Strait of Hormuz, (2) undertake unilateral and proxy terrorist attacks on multiple continents, and (3) conduct long-range strikes using its own missiles or by way of long-range rockets and short-range missiles in the hands of proxies such as Hizballah. Iran’s growing cyberwarfare capabilities may eventually become a fourth leg of this deterrent/warfighting triad, enabling it to strike at adversaries and to project power globally, instantaneously, and on a sustained basis, in ways it cannot in the physical domain.
Read more on Washington Institute for Near East Policy: http://www.washingtoninstitute.org/policy-analysis/view/the-role-of-missiles-in-irans-military-strategy