Targets Near and Far
The forces fighting against the Saudi-led coalition have applied their ballistic missile arsenal in two distinct manners. First, they have used the missiles tactically to increase the cost of intervention on the Saudi and United Arab Emirates forces, primarily while they operate in Yemen. Shorter-range ballistic missiles such as the Russian-made Tochka missiles have been used to target foreign bases and logistics points in Yemen. Some missile strikes have done extensive damage, destroying equipment and supplies and killing up to several dozen foreign troops.
Houthi and Saleh loyalists have also applied them in a strategic fashion, launching missiles into Saudi Arabia to try to deter the Saudis from conducting military operations in Yemen. Most of these missiles have targeted Saudi military positions in the provinces bordering Yemen, though Houthi forces also claim to have launched several missiles deep into Saudi Arabia, targeting Mecca and Riyadh. Saudi Arabia operates U.S.-made Patriot missile defense systems, which reportedly have intercepted a large number of missiles, and Riyadh has denied being struck. Raytheon, the Patriot's manufacturer, has backed up Saudi statements by claiming a 100 percent success rate for its systems in Saudi service.
A Seaward Deterrence
At the end of 2016, Houthi rebels also launched a number of anti-ship cruise missiles at vessels belonging to the Saudi-led coalition and the U.S. Navy. While these missiles are different from the ballistic missiles used against forces on the ground, and against targets in Saudi Arabia, their use reinforces the perception of an advanced missile threat originating from Yemen. Consequently, when Houthi loyalists fired anti-ship missiles at U.S. Navy vessels in October 2016, the United States responded by firing cruise missiles at coastal radar sites in areas under Houthi control. In January 2017, coalition forces recovered important coastal territory near the Bab el-Mandeb strait as well, which helped mitigate the missile threat to naval vessels. Except for one attack in June, these actions have deterred further anti-ship cruise missile attacks so far.
There has been no similar deterrence when it comes to the ballistic missile threat. Despite the coalition's air campaign, and claims by Saudi Arabia during certain points of the conflict that it had destroyed most, if not all, of the missile stockpiles in Yemen, the Houthi and Saleh loyalists continue to launch ballistic missiles. Their continued use could mean there is a gap in the intelligence available to the Saudi-led coalition, and that there are remaining stockpiles that are not known and have not been destroyed. Or, it could mean that the rebels are still able to import or even produce their missiles. The coalition has imposed a blockade on Yemen, making it difficult to ship this type of missile into the country, but perhaps not impossible. Critical parts used in modifying or building missiles could be smuggled through the blockade.
Where Missile Modifications Sometimes Go
Before the conflict, Yemen's missile forces, which were part of the Republican Guard units loyal to Saleh, used a number of different ballistic missiles. Those missiles that were officially known to be in the Yemeni arsenal were Russian-produced Scud and Tochka missiles, as well as unguided Uragan 220 mm artillery rockets. The Yemeni military also operated a large number of Russian-made, unguided Luna-M artillery rocket systems, but these allegedly were removed from service before the current conflict. In addition, Yemen was also known to operate a number of North Korean-built Hwasong-6 missiles, as the Spanish navy intercepted a shipment in 2002 that eventually was let through. The Hwasong-6 is essentially an improved Scud, its range extended by lengthening the missile and its internal propellant tanks.
Today, however, Houthi and Saleh loyalists talk of using entirely different types of missiles in their attacks, most notably the Borkan-1, Borkan-2, Qahir and Zelzal-2 missiles. None of these missiles is known to have existed in the Yemeni arsenal before the conflict, and only one of them, the Zelzal, was known to have existed at all. The Zelzal is an Iranian-produced missile based on the Russian Luna-M artillery rocket system. Some observers have suggested Iran may be smuggling these missiles into Yemen, though Yemeni claims that the Zelzal-2 missiles are indigenously produced suggest they could be modifying versions of the older Luna-M rocket systems. The Qahir missiles, meanwhile, are Russian-designed SA-2 air defense missiles that have been modified to strike ground targets.
The Borkan missiles are also likely modifications of missiles previously in the Yemeni arsenal. In pictures, the missiles appear to be similar in shape and dimensions of Scud missiles. Yemeni forces are likely modifying Scud missiles in the same way North Korea, Iran and Iraq did before them. By using parts of multiple Scuds, the internal propellant tanks can be lengthened, extending the missile's range. If a number of these Borkan missiles really are capable of reaching Mecca, Riyadh or other cities, as claimed, regardless of whether they strike their targets, then Yemeni engineers really are pushing the boundaries of what simple modifications to Scud missiles can achieve. Simply stretching out the Scud missiles to extend the range that far would cause issues with balancing the missile, powering its electronics and maintaining sufficient degrees of accuracy. At that point, the missiles need to be redesigned internally, rather than simply extended. It's unclear whether Yemeni engineers are redesigning the missiles, but as the missile's capabilities are expanded, the trend moves away from modification toward redesign.
In other countries, such a process has led to independent, indigenous missile development programs. North Korea and Iran both started by modifying Russian-built missile systems before developing their own longer-range alternatives. It's important to note, however, that at this point no capabilities beyond missile modifications have been observed in Yemen. Under the constant pressure of the Saudi-led air campaign, it is currently unlikely Yemen could develop a full-fledged missile development program, and reports suggest the Yemenis are relying on outside experts — from Iran, for example — to make even the simpler modifications to their existing missiles, raising additional questions about Yemen's indigenous capabilities. The ballistic missile threat from Yemeni rebels will continue to depend on remaining missile stockpiles, or on imports from Yemen's allies.