The present conflict in the Red Sea has, for the first time, brought the world’s attention to the potential of low-cost drones in naval warfare. Many commentators have expressed surprise that the Houthis, by employing a new generation of cost-efficient weapons, have been able to exert sea denial and drain the coffers of the mighty U.S. Navy. This is true, but it is also beside the point; American resources are so much greater than the resources of Yemen that the United States can prevail regardless of inefficiency. The question we ought to be asking is not “what can Yemen achieve with these new weapons,” but “what can China do with equivalent or better weapons?”

The consensus that SM-2 and ESSM surface-to-air missiles (SAMs), fighter aircraft, and five-inch guns are now being used to engage kamikaze drones in the Red Sea is concerning for the United States. For example, the Iranian Shahed-136 drone, which has been extensively used in Ukraine, has an estimated range of 1,350 nautical miles, has reportedly been used to attack ships at sea this year, and reportedly costs no more than $50,000. In the context of naval warfare, it is misleading to characterize these weapons as drones; they are, in fact, a new class of cheap anti-ship missile (we will call them CASMs) potentially far more effective than the flashy, expensive anti-ship ballistic missiles which have attracted so much more attention in the past decade. No existing kinetic defenses are even remotely suitable for engaging such weapons.

The Inadequacy of Current Kinetic Defenses

Traditionally, warships have been defended from incoming anti-ship missiles by surface-to-air missiles, which trade short range for high speed and accuracy. As a consequence of these tradeoffs, naval SAMs are generally of the same order of cost as the anti-ship missiles they are intended to intercept.

To take the current U.S. examples: the Harpoon Block II anti-ship missile costs roughly $1.4 million; short-ranged ESSM SAMs cost about $1 million; and long-ranged SM-2s cost about $2 million. However, since the destroyers that these SAMs protect cost about $2 billion apiece and can only carry a limited number of SAMs (up to 96 SM-2s or 384 ESSMs), intercepting the missiles is not a sufficient defense. 714 Harpoon missiles, costing only half as much as the destroyer, would overwhelm the destroyer’s defenses. By comparison, the same investment would buy the attacker 20,000 CASMs. 

High explosive guns and cannons provide a more cost-efficient way of intercepting slower missiles. Still, they will only have time and ammunition to intercept a small number, even if they are accurate. For example, assuming that the 5-inch gun on a Burke-class destroyer could engage aircraft at a range of up to 20 nautical miles, it will have twelve minutes to intercept drones flying at 100 knots before they impact the ship. With a maximum fire rate of 20 rounds per minute, the gun could destroy a maximum of 240 incoming drones in this time, even if 100 percent of the rounds hit. Fighter aircraft with air-to-air missiles and guns are another option, but current air-to-air missiles are too expensive, and internal guns lack the ammunition to destroy more than 20 CASMs per sortie. Hence, if we again assume 20,000 CASSMS fired at one destroyer, it would take over 600 fighters to protect a single ship.

Due to the relative cost inefficiency of kinetic defenses, naval forces have traditionally taken one of two approaches to ensure survival: either “shoot the archer”—that is, destroy the missile’s more expensive launch platform, such as an aircraft or warship before it can release its payload—or stay outside of the enemy launch platform’s range in the first place. In the case of the conventional Harpoon missile with a range of only eighty nautical miles, the defender can combine both approaches to ensure survival. We can, therefore, see why CASMs pose such a serious potential threat: their 1,000+ nautical mile range allows them to be launched inland from mobile, dispersed, inexpensive ground launchers (read: trucks), which are no more attractive targets than the missiles themselves. It is also impossible to stay outside their effective range if, for instance, the objective is to escort merchant ships to Japanese and Taiwanese ports.

Considering the fundamental limitations of kinetic defenses, the best option available to the defender is to use electronic warfare (EW)—either to jam the link between missiles and their controllers (which is likely effective against current but not near-future threats) or to fry their circuits. EW is a good solution for two reasons: it can be effective at longer ranges than guns, and a single EW array can engage many missiles simultaneously. Because of these advantages, EW will likely be the primary counter against CASMs, at least until dedicated interceptor drones are developed. However, the evident ability of extremely cheap drones (costing just hundreds of dollars) to remain effective on the front lines of Ukraine despite enemy jamming does not bode well for the ability of current naval EW suites to reliably deal with CASMs costing tens or hundreds of thousands of dollars. 

Because of their meager cost and complexity, there is little doubt that a state like China could suddenly ramp up production of these new missiles to acquire hundreds of thousands or millions in a matter of months. As such, even if the drone swarm threat is not real yet, it could materialize in a very short space of time. Simply waiting for new capabilities to counter the threat is unsatisfactory, especially since CASMs are already completely mature. Still, even when the new defenses are equally advanced, their deployment will likely require significant work on the Navy’s surface combatants, which will take a long time. 

A Potential Stopgap: Improvised Interceptors

As we have outlined, early detection of attacking drone swarms is no solution unless there is a cost-effective method of actually attacking the CASMs at range; otherwise, defenses will simply be exhausted by attrition. Electro-magnetic pulse (EMP) weapons could be useful. Still, they could easily be countered by dispersing the swarms in both space and time unless it is also possible to engage dispersed missiles effectively.

Attaching gun pods and rudimentary gunsights to low-performance manned aircraft is one potential stopgap solution. For instance, the SUU-16 gun pod used on the F-4 Phantom had a capacity of 1,200 rounds and fired at a rate of 6,000 rounds per minute—much faster than the rate needed to engage slow aircraft. Many pods with their fire rates reduced to achieve the same burst mass could achieve the desired effect, with sufficient ammunition to destroy, say, 100 CASMs between four double-capacity gun pods firing at 600 rounds per minute. As for platforms, the V-22 Osprey is one seemingly attractive option. At 250 knots, it is fast enough to intercept slow targets like the Shahed 136 (100 knots). It has sufficient range (and refueling capability) to operate from either dispersed land bases or warships while protecting shipping. Due to its vertical lift capabilities, it could match speed with slower targets, providing for relatively good gunnery. Most importantly, there are already 400 of these aircraft, and bolting gun pods and simple gunsights on them ought to be a relatively cheap and low-risk enterprise.

Clearly, such improvised interceptors are not an adequate solution to the CASM threat. If, for example, we assume that a fleet of 400 Ospreys could each destroy 100 Shahed-type CASMs per sortie, then they could only defeat a swarm of 40,000 missiles—which would cost the attacker $2 billion, or as much as one destroyer. Of the currently available options, EW is the only means that is likely to be effective against CASMs. However, the evidence from the Red Sea suggests that current EW capabilities might not be sufficient or might not be usable in low-intensity conflicts due to the need to preserve their secrecy against China and Russia. Improvised interceptors might provide a measure of redundancy and overlap with existing EW capabilities, bridging the gap between the cheapest CASMs (presumably the most susceptible to EW) and more expensive traditional missiles, which have traditionally been engaged by SAMs. Furthermore, improvised interceptors might allow the United States to avoid using its EW capabilities in low-intensity conflicts like the present one in the Red Sea. Ultimately, the combined improvised interceptor/EW package could buy a little time for new technologies to mature to the point where they can provide a comprehensive defense, assuming that adversary CASM procurement is cost-efficient and, therefore, takes many months to ramp up to sustained levels. 

The Real Solution: War Stockpiles

In the case of rapid Chinese procurement of CASMs—or in the case that existing defensive capabilities cannot keep pace with the threat—a temporary blockade of the First Island Chain might be unavoidable. If so, the only solution may be to divert a portion of the combined defense effort toward accumulating much larger stockpiles of food, fuel, war supplies, and other essentials in the First Island Chain—especially Taiwan—allowing the allies to hold out until technological adaptations can break the blockade. Such an effort would also hedge against other kinds of unexpected offensive breakthroughs (such as by much more technologically advanced boost-glide missiles), which may be impossible to counter by an ad-hoc expedient such as the one we have proposed for CASMs. In 2021-2022, it was reported that Taiwan’s overall food stocks were sufficient for “at least” six months, coal for thirty-nine days, oil for 146 days, and natural gas for eleven days. Taiwan’s total agricultural imports in 2021 amounted to $14.8 billion, coal $16.2 billion, and oil $31 billion, for a total of $62 billion—equal to about 7.5 percent of total U.S. defense expenditures in that year. Between them, Taiwan, Japan, and the United States evidently have the resources to greatly expand the war reserves of the First Island Chain, even to the point that waiting for technological adaptations before trying to run the blockade would be a viable option.