The Chairman of the Joint Chiefs of Staff has expanded the language of modern warfare far beyond the traditional battlefield. Gen. Dan Caine told the Air, Space, and Cyber Conference that the American joint force must be prepared to fight, endure and win "from the seabed to cislunar space." Cislunar space is that region between the Earth and the moon.
That does not mean American troops are about to establish military positions on the Moon. It does mean that the enormous region between the Earth and Moon is increasingly being treated by military planners as a potential theatre of strategic competition.
This development should not be dismissed as science fiction. The United States, China and other powers depend increasingly upon satellites for communications, navigation, surveillance, missile warning and military command. As human and robotic activity extends towards the Moon, military interest will inevitably follow.
Cislunar space broadly refers to the region extending beyond conventional Earth orbit towards the Moon. Definitions differ over precisely where it begins and ends, and whether discussion of the cislunar domain includes the lunar surface itself. The important point is that American defence planners are now thinking seriously about security well beyond geosynchronous orbit, approximately 36,000 kilometres above Earth.
The immediate military issue is not soldiers fighting in lunar craters. It is surveillance. Space is not strategically uniform. Certain orbits, trajectories and locations are far more valuable than others. Communications with spacecraft operating on the far side of the Moon require relay systems because the Moon itself blocks direct radio contact with Earth. Objects travelling between Earth and lunar space can also be difficult to detect and continuously track using systems designed primarily for objects in conventional Earth orbit.
China's growing lunar program therefore has an unavoidable strategic dimension, irrespective of its scientific achievements. China has operated spacecraft on the far side of the Moon and has deployed relay satellites to maintain communications with them. These are legitimate scientific accomplishments. They also demonstrate technologies and infrastructure that could have military applications.
This is the familiar problem of dual-use technology. A spacecraft designed to inspect another satellite can potentially provide valuable scientific or maintenance services. The same spacecraft might also approach an adversary's satellite. A powerful laser might be used for communications or ranging, while similar technology could potentially interfere with optical sensors. A lunar communications relay can support scientific exploration while also providing infrastructure useful to military operations.
The central American concern is therefore knowledge. If an object leaves high Earth orbit and travels towards the Moon, military commanders want to know where it is going, what it is doing and whether it represents a threat. This requires extending what the Space Force calls space domain awareness much farther into cislunar space.
There is also an unresolved legal problem. The 1967 Outer Space Treaty was written during the Cold War, when permanent human activity on the Moon remained largely theoretical. Article IV prohibits the establishment of military bases, installations and fortifications on celestial bodies. It also prohibits weapons testing and military manoeuvres there. The Moon and other celestial bodies are to be used exclusively for peaceful purposes.
But the treaty does not exclude every military activity. Military personnel may be used for scientific research or other peaceful purposes, and military equipment may likewise be employed for peaceful exploration. That distinction becomes increasingly difficult as technology develops.
Suppose a lunar installation officially exists for communications and scientific observation but also provides military surveillance. Is it a scientific facility with a secondary defence function, or a military installation prohibited by the treaty? What about a spacecraft capable of servicing satellites that could also disable them? What happens when a civilian lunar transport system carries military equipment? These are no longer purely academic questions.
The greatest danger may arise well before anyone attempts to establish a conventional military installation on the Moon. Competition is more likely to begin with surveillance systems, communications networks, electronic warfare capabilities and spacecraft capable of approaching or interfering with other spacecraft.
Kinetic weapons would be particularly dangerous. Destroying satellites can produce debris that threatens other spacecraft. In some orbital environments such debris can remain hazardous for very long periods. Extending such warfare into cislunar space would introduce another layer of uncertainty because trajectories are more complicated and there is no atmosphere conveniently waiting below to remove much of the debris.
This is why the militarisation of cislunar space deserves attention now. The United States is likely to develop better sensors capable of detecting and tracking objects travelling between Earth and the Moon. Commercial lunar landers and space tugs will probably acquire increasing national-security significance. Military planners will have to decide how attacks upon communications relays, navigation systems and surveillance spacecraft should be classified and answered.
American allies will eventually face the same questions. Australia, Britain and Japan already cooperate closely with the United States in defence and intelligence. If Washington develops an extensive cislunar surveillance architecture, pressure for allied participation is predictable. Australia could eventually find itself contributing ground stations, tracking facilities, communications infrastructure or intelligence rather than anything resembling a conventional lunar military force.
China will naturally interpret American developments through its own security interests, just as Washington interprets Chinese lunar infrastructure through American interests. That creates the classic security dilemma. One side deploys surveillance equipment because it fears being surprised. The other sees that surveillance network as preparation for military dominance and responds with additional capabilities. Each side then cites the other's response as proof that its original fears were justified.
There is another reason for caution. Cislunar military operations would be extraordinarily expensive. Every spacecraft sent deep into the Earth-Moon system requires launch capacity, energy, communications, tracking and logistical support. Money spent building an elaborate military presence around the Moon is money unavailable for ships, aircraft, missiles, ammunition and other capabilities that may be considerably more important in an immediate Western Pacific conflict.
China understands this calculation as well as the United States. A competition for dominance in cislunar space could become strategically important. It could equally become an enormously expensive diversion.
Nevertheless, the basic problem identified by Caine cannot simply be ignored. Modern warfare depends heavily upon space systems. Once major powers establish significant infrastructure beyond conventional Earth orbit, military planners will inevitably consider how to protect their own systems and monitor those of potential adversaries. The sensible objective should therefore be limited and defensive.
The United States and its allies need sufficient surveillance capability to know what is operating in cislunar space. Rules governing interference with spacecraft and non-kinetic weapons should be developed before a crisis forces governments to improvise them. Existing treaty obligations concerning the peaceful use of the Moon should be defended rather than quietly abandoned as military technology advances.
Most importantly, governments should resist allowing the language of inevitable military competition to become a self-fulfilling prophecy. There is a considerable difference between possessing the ability to detect potentially hostile activity around the Moon and treating the entire Earth-Moon system as simply another battlefield waiting to be occupied.
Gen. Caine's statement matters because it reveals how far American strategic thinking has already moved. For most of the Space Age, military competition centred upon Earth orbit. The conceptual boundary is now being pushed towards the Moon.
There will probably be no Marines fighting from lunar craters anytime soon. The more realistic contest will involve sensors, communications, surveillance, electronic interference and control of strategically valuable positions and trajectories. That may sound less dramatic than a war on the Moon. In strategic terms, it may prove considerably more important.
https://www.defenseone.com/threats/2026/09/pentagon-battles-moon-joint-chiefs-chairman/416021/