The common claim that Iran’s missile development must be stopped altogether because these systems could deliver nuclear weapons in the future rests on broad generalizations. While there is reason for concern, priority attention should be given to those missiles that might realistically be used for such a purpose, if Iran were to go down a perilous nuclear path.
The international standard – but not treaty – for determining the inherent nuclear capability of missiles is the threshold developed in 1987 by the Missile Technology Control Regime (MTCR), which seeks to forestall exports of missile systems able to deliver a 500kg payload a distance of 300km or more. Eight of Iran’s 13 current ballistic missile systems – the largest and most diverse arsenal in the Middle East – exceed this threshold and are thus deemed to be nuclear capable. The other five, all within the Fateh-110 family of missiles, are certainly lethal, especially when shipped to Hezbollah for use against Israel, but they are clearly not intended for nuclear use.
Because capability does not equal intent, the MTCR guidelines should be just the first step in an assessment of Iran’s intentions for its missiles. When the United Nations Security Council drafted a new resolution in July 2015 to accompany the Iran nuclear agreement finalized that month, an element of intent was added to previous sanctions resolution language that prohibited launches of Iranian missiles that were ‘capable of delivering nuclear weapons’. The 2015 resolution calls upon Iran not to engage in activity concerning missiles ‘designed to be’ capable of delivering nuclear weapons.
What it means ‘to be designed’ is undefined. Judging intent is partly subjective, but technical clues and intelligence information can guide analysis. The soundest approach is to disaggregate Iran’s various missile systems, and to assess design intentions on the basis of the technical capabilities and lineage of the different missiles.
Assessing Design Intentions
We note that two of Iran’s short-range missiles – the Shahab-1 and Shahab-2 – are based on Soviet export-model Scud-Bs and -Cs that were designed to carry conventional weapons. These systems exceed the MTCR threshold and are thus inherently capable of carrying nuclear weapons. It would be incorrect to claim, however, that they were designed for this role. Iran’s reason for first acquiring these systems in the mid-1980s – to retaliate against Iraq’s missile attacks against Iranian cities – underscores their purpose in delivering conventional warheads.
At the other end of the scale in terms of intent, there is strong evidence that Iran’s Ghadr system was indeed designed with a nuclear payload in mind. As has been well reported, the schematics on a computer hard drive turned over by a defector in 2004 demonstrate efforts to redesign the re-entry vehicle of the Shahab-3 to accommodate what appears to be a nuclear implosion weapon. The solid-fueled Sajjil-2 and the liquid-fueled Qiamhave the same baby-bottle shaped nosecone and thus were also presumptively designed for nuclear-weapons delivery. The case for the Qiam, however, is less clear, because it appeared several years after the tell-tale intelligence surfaced.
A conclusion that the Ghadr was designed for nuclear-weapons delivery is also supported by its North Korean Nodong origin. The Shahab-3, which is the name that Iran gave to the Nodongs it imported, also appears to have been designed for nuclear weapons. It is not entirely clear whether Nodongs originated in North Korea or the Soviet Union, but in either case they were developed to deliver nuclear weapons. Iran’s Emad missile is a 2015 variant of the Ghadr, and thus by its lineage was arguably designed for nuclear weapons. It has a different nosecone, however.
Iran’s medium-range Khorramshahr missile is harder to judge, because of the dearth of good information and successful test launches. It appears to be derived from North Korea’s Musudan, which employs technology and hardware originally designed for the Soviet Union’s R-27 submarine-launched ballistic missile. Both the Soviets and North Korea designed the R-27 and Musudan, respectively, to carry a nuclear weapon. We, therefore, tentatively judge the Iranian versions of this missile to be designed for nuclear-weapons delivery.
In addition to its ballistic missiles, Iran has developed two space-launch vehicles, the Safir and Simorgh. Both carrier rockets are optimized for launching satellites, and are not well suited to perform as a ballistic missile. Neither rocket has been tested as a ballistic missile and would require modifications for such a use. It is, therefore, hard to make the case that the Safir and Simorgh are designed to be capable of nuclear-weapons delivery. To the contrary, they were designed and configured to be satellite launch vehicles. It should be noted that no country has converted a satellite-launch vehicle into a long-range ballistic missile.
Focus on Medium-Range Systems
In light of the central role that ballistic missiles play in Iran’s defense and deterrence posture, especially given its antiquated and inferior air force, it is inconceivable that Tehran would voluntarily agree to surrender them entirely. The United States and its allies should give greatest priority to curtailing Iran’s medium-range systems that most clearly were designed to deliver nuclear weapons, and be prepared to accept missiles that clearly were not, including both the short-range system and space-launch vehicles.
Drawings and descriptions of a nuclear-implosion device mounted inside a Shahab-3 nosecone that Israeli Prime Minister Benjamin Netanyahu unveiled on 30 April 2018 prompted an update to our assessment. The nuclear bomb, as depicted in the captured Iranian files that he displayed, has an estimated diameter of 585 mm. The diameter of the depicted Shahab-3 nosecone that corresponds to the maximum width of the nuclear bomb is about 720 mm. The gap between the nuclear device’s outer surface and the nosecone’s inner surface is needed for fixtures that secure the bomb within the warhead and material designed to insulate it from the thermal and vibrational loads experienced during flight, including atmospheric re-entry. This information, along with the documentation contained on a laptop smuggled out of Iran in 2004, suggests that Iran’s presumptive nuclear-bomb design was intended for use on a Shahab-3 missile.
However, the 585-mm bomb design cannot be fitted into the narrower nose cone of the Ghadr, Sajjil, and by extension, the Qiam missiles. The modified, triconic nosecone of this system was initially revealed during a flight test in 2004, after revelation of the laptop documents. We therefore now judge that the Ghadr, Sajjil and Qiam missiles were not specifically designed to carry nuclear warheads, but rather, conventional weapons. This conclusion would need to be adjusted if Iran were able to develop or acquire designs for a smaller nuclear warhead.