A propulsion disabler (PD) is a small, passive, torpedo-like device that serves as a cheap, non-lethal mine and torpedo warhead. The proposed munition’s purpose is to destroy a ship’s external propulsion or direction-control mechanisms, leaving the vessel stationary. Production of PDs is possible with today’s emerging robotics technologies. Future PD devices could be used in an autonomous swarm that combines the smallest explosive charge with the greatest disabling effect by attacking a ship at its most vulnerable point.
Once PDs become widely available, they may well be the weapon of choice by all navies against civilian ships. Similarly, disabling an enemy’s naval ship rather than sinking it will almost always be the superior choice, certainly for the U.S. Navy. The logic that makes this so will compel adversary navies to make the same choice.
The PD could see extensive use in the Taiwan war scenario described by the American Seapower Project. It also could play a role in any follow-on war with China, and in current so-called grey-area conflicts.
PDs are not yet known to exist. No signs in the public domain suggest the U.S. intelligence community is aware of any PD, but it is hard to imagine an asymmetric capability more attractive to China, Russia, or, especially, to lesser powers such as Iran. They appear to be fairly simple and inexpensive to manufacture, as well as hard to defend against. Weaker opponents could use them to neutralize the surface ships of more powerful navies. The PD is a strategic weapon that will make existing blockade strategies easier to carry out, and new strategies necessary.
Propulsion Disablers in Defense of Taiwan
The potency of the PD can be understood when analyzed in the context of the American Seapower Project. Set in 2026, the scenario places Chinese forces fighting on Taiwan and receiving logistical support from the mainland by sea—the only way support can come in the volumes needed.
If Taiwan’s defenders deployed PD mines in this hypothetical scenario, some of China’s amphibious landing ships would be disabled, leaving them to drift helplessly and exposing perhaps several thousands of hungry marines to attack by defenders from the air, at and under the sea, and from shore—delivered at whatever time the defenders choose. Chinese tugs or warships sent to retrieve disabled ships would risk being disabled themselves, making the attackers’ situation worse. Supporting logistics ships would face the same threat, assuming defenders could reseed depleted PD minefields. In sum, PDs would pose a significant threat to ships involved in the scenario’s initial attack, and to all ships that came later.
Propulsion Disablers in General Use
Characteristics
Propulsion disablers would be critically affordable for a potentially lengthy war of attrition at sea against China, the world’s leading shipbuilder. Their small size has multiple benefits: It makes them efficient to deploy and to use at scale as mine warheads. Crewed and uncrewed submarines might deploy many hundreds of PD mines from modules already under development or introduced in the future. Cruise or ballistic missiles could deliver significant numbers of PD torpedoes, extending their range of threat and possibly inundating defenses.
Aircraft could seed PD mines rapidly over a wide area. As torpedoes delivered from a wide variety of platforms and means, including anti-ship missiles fired from shore, PDs would target naval and civilian ships, including container ships, liquefied-natural-gas carriers, big fishing ships, scientific research vessels, and other types. A tanker hit by a PD would be unlikely to spill much, if any, of its liquid cargo, thus sparing damage to the seas, islands, and adjacent littorals. Against large warships like those in Western navies, PDs might be employed singly. But swarms of PDs would seek to saturate defenses from multiple azimuths, overwhelm countermeasures, and increase the probability that multi-screw ships could be completely disabled.
PDs would be as smart as modern information and robotics technologies can make them. They would employ a library of sonic signatures of the naval and civilian ships of adversaries, those of partners and allies, and above all, U.S. Navy ships. The ideal PD could distinguish between friendly and enemy ships and those of third parties, as well as between categories of ships, allowing it to avoid targeting ferries and passenger ships.
The technologies that ensure future PD capabilities can also be turned against them. PD mines are hardly invulnerable. Cheap, mass-produced, simple robot minesweeping platforms, effective against mines of all kinds, seem within reach today.
Physical Consequences of Employment
Ships depend on mobility to accomplish their purpose. In the case of civilian ships, that purpose is mainly to move commercial cargo. In the case of naval ships, it is mainly lethality. Depriving a naval ship of its mobility has essentially the same result as sinking it: the ship loses its lethality against targets beyond the range of onboard weapons. It also makes the ship itself a stationary target.
Although PDs are less violent than torpedoes, they are not benign. A ship helpless before an unforgiving sea would present its owner (and the disabling party) with complex choices regarding the use of available forces. The owner would first be concerned with rescuing the crew, and then with recovering the ship and cargo, but might lack the means to do either. In that case, those tasks would fall to the disabling party who, as a matter of moral, political, and likely legal obligation, could not be indifferent to the fate of those its attacks have put at risk. The attacker would have to expend resources to seize disabled enemy merchant ships, and to intern as prisoners of war the crews of disabled naval ships.
Employing PDs creates a new way of fighting. Rather than attacking to sink the enemy’s naval ship, a better choice might be to PD it. A potential enemy like China presents many thousands of civilian and naval targets at sea and has the capacity to produce many thousands more, especially uncrewed platforms, which require no trained people to operate them. PDs are ideal in this kind of conflict.
Three advantages favor use of PDs against naval ships:
1) It makes the ship vulnerable to seizure for intelligence exploitation, while crews can be made POWs.
2) The ship becomes a globally visible symbol of the enemy’s weakness and the attacker’s superiority, highly valuable for diplomatic and information-warfare purposes.
3) Both sides would be forced into actions to protect and rescue disabled ships.
This last reality will produce new scenarios for combat engagement. Each side is fighting, as always, to dominate the other and to determine general command of the world ocean. But now commanders must determine the fates of disabled ships. The disabling side will define where any combat takes place and with what weapons. China would use PDs against ships in zones covered by its anti-access/area-denial systems. Wisely employed, PDs would leave the United States and its allies with little choice but to fight under quite unfavorable conditions.
Political Consequences of Employment
Western naval ships will almost certainly be attacked by PDs for political purposes in the grey-area combat commonly encountered today. They are an almost perfect weapon for use by the weaker side in circumstances where responsibility for the attack may be plausibly denied. U.S. Navy and allied ships are vulnerable to PD attack in the Middle East because their missions require them to operate in near-shore waters. U.S. ships on Freedom of Navigation Operations in the South China Sea are equally vulnerable. Washington should immediately prepare military and political reactions to a future PD attack against ships of the U.S. Navy and those of allies and partners.
Attacks on Western naval ships were completely unforeseen in the original thinking about the PD. The propulsion disabler concept first emerged in the search to make a Western blockade strategy affordable and sustainable, and to solve the moral, political, and legal problems involved in a blockade. The advantages of using PDs against naval ships make it nearly certain that PDs will be used against U.S. ships, and those of its allies and partners. Developing defenses against the PD is a priority as high as fielding the weapon in the first place. The PD may prove transformative. Coupled with uncrewed robotic weapons, it will have far-reaching effects. Both sides will fight over disabled naval ships, with the disabler enjoying significant advantages. The PD will make blockade against economic shipping operationally feasible and politically acceptable, affecting the course and possible outcome of major wars and profoundly affecting international shipping.
Suggested Actions
- Develop PD capabilities to support the offensive and defensive strategies suggested here. Exploit robotics technologies to the fullest.
- Plan for the protection of the surface Navy and ships of allies against PD attack—immediately in the Middle East and the South China Sea. Anticipate physical actions and prepare verbal policy in response.
- Evaluate the potential of PD mines and torpedoes in an antisubmarine role.
- Direct the intelligence community to search for signs of adversary PD development, including in their open military writings.
- Ensure that intra-Navy research, analysis, and gaming address PD/counter-PD issues. Request the Intermediate Force Capabilities Program to similarly adjust its focus.
The probability PDs will soon appear is high, and their introduction will likely transform naval warfare. The United States should develop and field PDs quickly for use in a potential defense of Taiwan, and for strategic use beyond. The PD will make blockade strategies physically more possible and politically more acceptable. PDs are unlike any weapon in use, and they will make new strategies necessary. It seems highly likely that adversaries will use PDs against the U.S. and allied and partner navies.
