The U.S. State Department approved an $11.25-billion sale last month of four Lockheed Martin “Multi-Mission Surface Combatants,” or MMSCs, for the Royal Saudi Navy. While the announcement is only for a “possible” purchase, the deal is likely to move forward given Saudi Arabia’s need to update its aging Persian Gulf fleet. The sale comes as the region faces growing uncertainty as result of the Iran nuclear deal and a decreasing American naval presence. These ships will be equipped to meet these challenges – but not the growing threat of Iran’s ballistic missiles.

The MMSCs are fast frigate-sized warships based on Lockheed’s Freedom-class littoral combat ship (LCS), currently in service with the U.S. Navy (USN). But unlike the troubled LCS concept – which has received criticism for being too lightly armed to survive a high-end conflict – the MMSCs will be better armed to combat a variety of high- and low-end threats. The Saudi ships will even feature greater air-defense capability than the USN’s replacement for the LCS.

The MMSCs’ armament includes Harpoon anti-ship missiles, Mk41 Vertical Launch Systems (VLSs) for anti-air Evolved Sea Sparrow Missiles (ESSM), a 76 mm gun (as opposed to the smaller 57 mm gun on the LCS), SeaRAM Close-In Weapon System (CIWS), Mk32 torpedo tubes, ten .50-caliber machine guns and a 20 mm Narwhal remotely operated gun system. It will use the same TRS-4D radar, COMBATSS-21 combat-management system, and WBR-2000 electronic warfare system of the American LCSs, as well as carrying at least one MH-60R Seahawk helicopter – which the Saudis requested in May. These systems combine to make the ship an advanced and lethal platform capable of handling just about any threat Iran or terrorist groups could pose.

Tehran’s military, after all, is decades and billions of dollars behind its Gulf rivals. Most of its air fleet consists of unflyable aircraft from the 1970s, while its navy relies on an asymmetric strategy that cannot survive a prolonged fight. However, Iran’s ballistic missile arsenal presents a real challenge.

The Islamic Republic has invested heavily in the development of multiple ballistic missile systems, including an anti-ship variant called the Khalij Fars (“Persian Gulf”). The Khalij Fars is based off of Iran’s Fateh-110, and allegedly can strike targets 300 kilometers away with a 650-kilogram payload. The Iranians also claim its guidance system is so advanced that it can strike within 8.5 meters of its intended target. While it is unknown whether Iranian claims regarding their missiles’ performance are accurate (after all, they have never seen use in combat), Gulf states and the U.S. should nevertheless be prepared for the possibility.

The MMSCs, however, are not properly equipped to defend against ballistic missiles. The ESSM missiles with which they will be armed are designed to shoot down hostile aircraft and cruise missiles (and strike some surface targets), but not ballistic missiles. The MMSC’s TRS-4D radar is also not suited for detecting and tracking ballistic missiles. These shortfalls will leave Saudi warships, oil infrastructure, and tankers vulnerable to potential attacks from Iranian anti-ship ballistic missiles.

A solution for this threat would have been to supply the USN’s Aegis ballistic missile defense (BMD) combat system, with its powerful AN/SPY-1 radar and advanced SM-2, SM-3, and SM-6 interceptor missiles – a system which the Saudis requested in February. Lockheed presented designs of the LCS with the Aegis combat system for export with the Gulf States in mind, and the MMSC design will already utilize the Mk41 VLS need to launch BMD missiles – all that is missing is the more powerful radar and the missiles themselves. Why they were excluded from the MMSCs remains unclear, but it likely has more to do with political sensitives than cost.

The principal reason to grant such a system to Saudi Arabia would be to ease the burden on the USN’s limited number of BMD ships. Currently there are only 33 USN cruisers and destroyers equipped for the BMD mission around the globe. Four of these ships are permanently forward deployed in Spain and routinely patrol the Black Sea and Eastern Mediterranean to defend Europe, as well as Israel, from Iranian ballistic missiles. At times a USN BMD ship will be deployed to the Persian Gulf, but like the current aircraft carrier gap, the Navy cannot maintain a constant presence because limited resources. In fact, the demand is so dire that Navy officials earlier this year called the current BMD strategy “unsustainable.”

The basic Aegis combat system has only been exported to a handful of America’s closest allies. Currently Japan, a stable U.S. ally which faces similar ballistic missile threats as Gulf states, is the only other country operating ships with the complete Aegis BMD capability. But Saudi Arabia is not Japan. Washington rightly has concerns about political stability in the Kingdom. Were Saudi Arabia to collapse altogether like some of its neighbors, a vital system developed to counter America’s most advanced foes could fall into the wrong hands and be transferred to the very adversaries it is meant to combat.

Selling such an advanced system to the Saudis also raises concerns that it would further erode Israel’s qualitative military edge (QME). The U.S. is already providing Saudi Arabia and other Arab states with some of the most sophisticated land-based missile defense systems available, including the Patriot PAC-3 and Terminal High Altitude Area Defense (THAAD) systems. But the Aegis BMD system has a longer range which may worry Israel, specifically the satellite killing SM-3 missiles. The U.S. could limit a Saudi system by only providing the shorter-range terminal-intercepting missiles (SM-2 Block IV or  newer SM-6), but they have additional land-attack capability that may also upset the Israelis.

In the end, with increasing constraints on U.S. defense spending and rising challenges around the world, augmenting American BMD ships with Saudi vessels capable of fulfilling the same role could ease the burden on the USN, and strengthen the Gulf missile shield that Washington has promised its GCC allies. But as instability continues to roil the Middle East, giving the Saudis such an advance capability may be a risk American policy-makers are not willing to take.

Patrick Megahan is a research analyst at Foundation for Defense of Democracies focusing on military affairs. He manages the website militaryedge.org