▌Source: “China Command and Control Society” WeChat Official Account
[Introduction] In recent years, the concept of ‘Multi-Domain Operations’ has become a hot topic in U.S. military research as a cutting-edge design recognizing future combat styles between major powers. To deeply study ‘Multi-Domain Operations’, one must first clearly define the most basic concepts of ‘domain’ and ‘multi-domain’. Although official documents have provided a preliminary definition of ‘domain’, there is still no fully unified view in the U.S. military theoretical community. This article begins by examining the historical and current understanding of the term ‘domain’ within the U.S. military theoretical community, combined with the definitions in official documents, and attempts to explore several issues that are crucial for accurately understanding ‘domain’.In recent years, the concept of ‘Multi-Domain Operations’ (Multi-Domain Operation Concept) has become a hot topic in U.S. military research as a cutting-edge design recognizing future combat styles between major powers. To deeply study ‘Multi-Domain Operations’, one must first clearly define the most basic concepts of ‘domain’ (Domain) and ‘multi-domain’. Although official documents have provided a preliminary definition of ‘domain’, the U.S. military theoretical community has not yet formed a fully unified view. Therefore, it is necessary to examine the current status and history of the U.S. military’s understanding of ‘domain’ and to explore what ‘domain’ is in ‘Multi-Domain Operations’.U.S. Military’s Understanding of ‘Domain’The current definition of ‘domain’ in official U.S. military ‘Multi-Domain Operations’ documentsSince it was first proposed at the Army Annual Meeting in 2016, the U.S. Army Training and Doctrine Command has issued three official documents on ‘Multi-Domain Operations’, including a white paper, Concept Version 1.0 and Version 1.5. With the strong promotion from the U.S. Army leadership and active participation from various military branches and combatant commands, the concept of ‘Multi-Domain Operations’ has been continuously developed and improved, and the definition of the term ‘domain’ in its official documents has also undergone some changes. For instance, the 2016 white paper ‘Multi-Domain Battle: Combined Arms for the 21st Century’ did not provide an accurate terminological definition for ‘domain’, but merely cited relevant statements in ‘Joint Vision 2020’ regarding the ‘air, land, sea, space, and information domains’; while the 2017 Concept Version 1.0 ‘Multi-Domain Battle: Evolution of Combined Arms for the 21st Century 2025-2040’ and the 2018 Concept Version 1.5 ‘The U.S. Army in Multi-Domain Operations 2028’ documents provided the same preliminary terminological definition in an appendix marked with an asterisk for subsequent improvement, stating that ‘domain’ is ‘a specific area involved in organizing and conducting operations within the overall operational environment, including land, maritime, air, space, and cyberspace domains.’ Specifically, the definitions of these five operational domains are as follows: — Land Domain (land domain), the area of the Earth’s surface that ends at the high water mark and overlaps with the coastal section of the sea; Maritime Domain (maritime domain), the oceans, ports, estuaries, islands, coastal areas, and the airspace above these terrains, including littoral regions; Air Domain (air domain), extending from the Earth’s surface upwards until the atmospheric effects on operational actions can be ignored; Space Domain (space domain), the airspace above a certain altitude where the atmospheric effects on aircraft become negligible; Cyberspace (cyberspace), a global domain in the information environment, composed of various interdependent information technology infrastructure networks and the data flowing within them, including the internet, telecommunications networks, computer systems, embedded processors, and controllers.2The preface of Concept Version 1.5 mentions, ‘The concept of ‘Multi-Domain Operations’ aims to contribute solutions for the U.S. to respond to the layered denial posed by peer competitors such as China and Russia across all domains.’ Here, the English expression for ‘all domains’ is ‘All 5 domains’, referring to the five operational domains mentioned above: ‘land, maritime, air, space, and cyberspace.’ In fact, it is not difficult to find throughout the U.S. military’s official documents on ‘Multi-Domain Operations’ that all references to ‘all domains’ or ‘multi-domain’ refer specifically to the ‘land, sea, air, space, and cyberspace’ domains, while the electromagnetic spectrum (Electromagnetic Spectrum) and information environment (Information Environment) are not included as ‘domains’, but rather expressed as part of the overall operational environment (Operational Environment).Historical Understanding of ‘Domain’ in U.S. Military TheoryDuring the research process, I found that the formation of the ‘five domains’ framework in the current ‘Multi-Domain Operations’ concept has not been achieved overnight. Over the past 20 years, with the continuous changes in the global strategic security environment and the corresponding adjustments in U.S. defense and military strategies, the U.S. military theoretical community’s understanding of ‘domain’ has been a process of continuous maturation and improvement.The U.S. military theoretical community places great importance on defining ‘domain’, believing that ‘domain’ delineates the boundaries of operational functions among various military branches, creating a reference framework for defining the preparation and conduct of warfare. Any military branch or institution must base its operational design or platform development on its dominant ‘domain’, and there are few preparations and practices that extend beyond their defined ‘domain’.4In 1996, against the backdrop of the great success of Operation Desert Storm, the Joint Chiefs of Staff issued the document ‘Joint Vision 2010’, which serves as the theoretical foundation for many subsequent joint operational directives. This document emphasizes the so-called ‘full-spectrum dominance’ in ‘defeating any adversary or controlling the battlefield in all types of military operations.’ At that time, the confident U.S. military believed it had absolute strength to defeat any adversary at any time and in any domain, and this vague understanding of ‘full-spectrum’ reflected the U.S. unipolar hegemonic thinking formed after the Cold War, supported by overwhelming military power. In June 2000, during the era of rapid development of information technology such as computers and the internet, the U.S. military issued the joint publication ‘Joint Vision 2020’, further interpreting ‘full-spectrum dominance’ as ‘the U.S. military should be able to conduct rapid, sustained, and synchronized operations… with the ability to intervene and operate freely in all domains (in all domains).’ This document contributed to the understanding of ‘domain’ in two ways: firstly, it was the first time the term ‘domain’ was included in a joint publication; secondly, it added the ‘information domain’ as an emerging operational domain to facilitate discussion and research on issues related to the information space, building on the traditional four ‘physical domains’ of land, sea, air, and space. The U.S. military believes that the information space will be an important domain for military operations in the 21st century, and the term ‘domain’ itself carries inherent meanings from the computer networking field, such as ‘domain names, file fields, and logical organizational units of operating systems or networks’, which provide natural advantages for understanding, communication, and dissemination in discussions of military operations in the information age, especially in the realm of cyber operations. Therefore, as the debates around military readiness in the information age continued, the term ‘domain’ gradually spread within the U.S. defense discourse system, and the Department of Defense, various military branches, combatant commands, and allies began to accept this new classification of operational domains.In 2009, the U.S. military published the ‘Joint Operations Capstone Concept’ (Version 3.0), officially replacing the term ‘information domain’ with ‘cyberspace’, proposing the classification of military operational domains as ‘land, sea, air, space, and cyberspace’, emphasizing that ‘whether in operational areas or the global commons, joint forces will maintain freedom of action across land, sea, air, space, and cyberspace.’5 This ultimately formed the ‘five domains’ framework in the official documents on ‘Multi-Domain Operations’.In recent years, with adjustments to national security strategy, the U.S. military has shifted its focus from completing anti-terrorism operations to deterring and winning potential military conflicts with major powers, giving rise to the ‘Multi-Domain Operations’ concept aimed at countering major powers such as China and Russia. As this concept gradually became a hot topic of discussion within military circles, debates regarding the term ‘domain’ have reignited. For example, compared to the tangible traditional physical operational domains such as ‘land, sea, and air’, how will the intangible ‘cyberspace’ and emerging ‘space domain’ be utilized in future conflicts between major powers? What is the basis for classifying ‘domains’? Where are the boundaries between different ‘domains’? The operational tempo, styles, and capabilities within different ‘domains’ vary greatly; how can true ‘multi-domain integration’ be achieved? What is the relationship between the electromagnetic spectrum, information environment, and the ‘five domains’? Some scholars have even proposed the addition of a ‘human domain’ within ‘Multi-Domain Operations’, arguing that the essence of warfare is the contest of wills between individuals, and the ‘ultimate measure’ of operational effectiveness across the domains is the degree of influence on human will. These various questions reflect the diversified attention and thoughts of the U.S. military theoretical community on the concept of ‘Multi-Domain Operations’, but they also indirectly indicate that defining ‘domain’ is not an easy task and requires a deeper understanding of its definition from multiple perspectives.
Several Key Issues for Accurately Understanding ‘Domain’ in Multi-Domain OperationsTracing back to its origins, the English word ‘Domain’ comes from the Latin noun ‘Dominus’ (lord, ruler), with its root ‘Dom-‘ originally meaning ‘the master of the house’, thus extending to meanings of ‘control, domination, and taming’. In the authoritative American Webster’s Dictionary, the term ‘Domain’ is defined as ‘complete and absolute ownership of land’, with common synonyms including ‘field, kingdom, territory, province, and estate’, while the term ‘dominance’ in U.S. military terminology is also derived from the same root as ‘domain’. It is evident that the term ‘domain’ carries a strong inherent meaning of ‘control and contention’.To accurately understand the official definition of ‘domain’ — ‘a specific area involved in organizing and conducting operations within the overall operational environment, including land, maritime, air, space, and cyberspace domains’ — one must grasp the following three key points: Firstly, ‘domain’ is born out of warfare, and focusing on combat is the fundamental attribute of ‘domain’; secondly, the classification of ‘domains’ must match military means; only when one possesses the capability to organize and conduct military operations in a certain ‘domain’ does the classification and existence of that ‘domain’ have value; lastly, ‘domain’ is part of the overall operational environment, and ‘multi-domain integration’ must be understood from a temporal and spatial dimension within the overall operational environment.Focusing on Combat is the Fundamental Attribute of ‘Domain’The definition clearly states that ‘domain’ is the activity area for organizing and conducting combat operations, and focusing on combat is the fundamental attribute of ‘domain’. Under the concept of ‘Multi-Domain Operations’, the future competition between nuclear powers and global counter-terrorism wars differ fundamentally; due to the significant changes in adversarial capabilities, the U.S. military’s absolute ‘multi-domain dominance’ no longer exists. The challenges faced by joint forces will shift from the use of ‘multi-domain’ to the contention of ‘multi-domain’, where the Army, Navy, Air Force, Marine Corps, Cyber Forces, and the emerging Space Force will engage in fierce competition with peer nuclear powers such as China and Russia across multiple domains including land, sea, air, space, and cyberspace. This competition includes both ‘non-kinetic effects’ such as intelligence collection, public opinion guidance, and psychological deterrence, as well as ‘kinetic effects’ involving armed conflict phases where conventional forces engage in intelligence reconnaissance, monitoring, and strikes, and integrated joint air defense systems. It can be seen that focusing on combat is the fundamental attribute of ‘domain’; only when opposing parties engage in fierce contention over a certain ‘domain’, either violently or non-violently, does the necessity for military classification and research of that ‘domain’ arise. Terms such as ‘human domain, psychological domain, and cognitive domain’ do not directly relate to the organization and implementation of combat operations but exert influence indirectly through the cumulative effects of operations in the ‘land, sea, air, space, and cyberspace’ domains, and therefore should not be considered as ‘domains’ defined in the U.S. military’s ‘Multi-Domain Operations’ concept.The Military Means is the Material Basis for Classifying ‘Domains’The definition emphasizes the organization and implementation of combat operations within ‘domains’, and this organization and implementation are closely linked to specific military means. The military means supported by certain technologies and equipment are an important material basis for classifying ‘domains’. Historically, in the thousands of years of human civilization conflicts, changes in the field of military confrontation have often accompanied waves of technological change: after the agricultural revolution, weapons such as stone axes, swords, bows and arrows, and catapults dominated the ‘land domain’ warfare for over 2000 years; with the advent of ships and the birth of navies, warfare began to extend into rivers, lakes, and seas, and the emergence of primitive weapons such as matchlocks and artillery, as well as more advanced firearms like rifled cannons after the 16th century, transformed naval combat from ‘boarding battles’ and ‘collision battles’ to ‘close-range fire attacks’ and ‘long-range bombardments’, significantly increasing the impact of ‘maritime domain’ military actions on war outcomes. After the 18th century, marked by the industrial revolution that began in Europe, the rear-loading rifled cannons replaced front-loading smoothbore cannons, smokeless powder replaced black powder, railways were used for military transport, and telegraph and telephone were used for military communications, with steam-powered armored ships racing across rivers and seas. The invention of airplanes in the early 20th century marked a historic leap in human warfare — transitioning from the ‘land domain’ and ‘maritime domain’ to the ‘air domain’, where fighter jets, bombers, and transport planes played significant roles in both World Wars, expanding warfare from ‘land and sea’ to ‘land, sea, and air’ dimensions. In 1946, under military commissioning, the University of Pennsylvania completed the world’s first programmable electronic digital computer, ENIAC, which greatly enhanced the U.S. military’s ballistic calculation capabilities. In 1969, to ensure that network communications could withstand the threat of a Soviet nuclear strike, DARPA collaborated with universities to develop ARPANET, the precursor to the internet. Since then, computer and internet technologies have rapidly developed, and major military powers have established ‘cyber forces’ to engage in fierce competition in the invisible battlefield of cyberspace through electronic spectrum interference, intelligence collection, cyber offense and defense, electronic countermeasures, and public opinion guidance. The ‘cyberspace’ domain has gradually become a key area of military confrontation. As for the ‘space domain’ mentioned in the ‘Multi-Domain Operations’ concept, given current technological levels and potential developments, reconnaissance, early warning, navigation, and communication satellite technologies are relatively mature, while advanced space combat equipment such as anti-satellite missiles, space bombers, space aircraft carriers, kinetic and directed energy anti-satellite weapons, and spaceplanes are still in experimental stages. However, it can be foreseen that as related technologies mature and are put into use, the ‘space domain’ will undoubtedly become a ‘high frontier’ for major power competition.In summary, with the development of military technology and equipment, the means by which humans engage in warfare have become more diversified, and the field of military confrontation has exhibited a pattern of expansion from ‘singular to plural, from flat to three-dimensional, from tangible to intangible’. Therefore, it is not difficult to understand that in order to facilitate discussions on how to upgrade from ‘joint forces’ to ‘multi-domain integration’, the U.S. military’s ‘Multi-Domain Operations’ concept classifies the domains of competition, armed conflict, and renewed competition among major powers into ‘five domains’, each of which is supported by corresponding military branches such as the Army, Navy, Air Force, Marine Corps, Cyber Forces, and Space Force. Material determines consciousness; separating the classification of ‘domains’ from specific military means is as absurd as asking a medieval knight to understand network-centric warfare, which easily leads to being devoid of substance and foundation.Understanding ‘Multi-Domain Integration’ from a Temporal and Spatial Dimension within the Overall Operational EnvironmentThe definition clearly states that ‘domain’ is part of the overall operational environment. To better clarify the relationship between the electromagnetic spectrum, information environment, and the ‘five domains’, and to comprehensively understand the complex interactions of various operational domains in time and space within ‘Multi-Domain Operations’, it is necessary to break away from the traditional thinking framework that a certain military branch dominates a specific operational domain, and to recognize and understand the five operational domains within a holistic operational environment.
According to the 2017 ‘Joint Publication 3-0: Joint Operations’ definition, the overall operational environment (Operational Environment) consists of various variable factors, situations, and influences that affect the use of joint capabilities and the decision-making of commanders, including physical domains such as airspace, land, sea, and space, the information environment (including cyberspace), the electromagnetic spectrum, and other systems related to specific joint operations, including hostile, friendly, neutral political, military, economic, social, information, and infrastructure systems. The nature and interactions of these systems will affect how commanders plan, organize, and conduct joint operations.
Figure 1: Description of Overall Operational Environment in U.S. Military Joint Publications
Firstly, the U.S. military does not categorize the ‘electromagnetic spectrum’ and ‘information environment’ as ‘electromagnetic domains’ or ‘information domains’, but rather understands them as important components of the overall operational environment, based on two main reasons: Firstly, the U.S. military believes that the ‘information environment’ is ‘a collective of individuals, organizations, and systems that collect, process, disseminate, or influence information’, consisting of three interrelated dimensions: physical, informational, and cognitive. The physical dimension, composed of communication networks, command systems, radio wave transmission towers, computers, smartphones, etc., serves as the material basis; the informational dimension emphasizes the collection, processing, storage, distribution, and maintenance of data; and the cognitive dimension reflects the ability of individuals to process, perceive, judge, and make decisions under the influence of information flow. If we liken the information environment to a complex system machine, then ‘cyberspace’ is like the external interface of this machine, embedded within the physical domains of ‘land, sea, air, and space’, where land-based, sea-based, air-based, and space-based operational platforms are interconnected through networks, and a large amount of battlefield situational awareness information in ‘cyberspace’ interacts with the information environment through physical dimension terminal devices. Therefore, ‘cyberspace’ is merely a part of the information environment, which encompasses a broader scope and cannot be defined as a specific operational domain; secondly, the U.S. military considers the ‘electromagnetic spectrum’ to be ‘the range of electromagnetic radiation from zero to infinity, specifically subdivided into 26 bandwidths such as microwaves, millimeter waves, and X-rays.’ As a strategic resource existing throughout the universe, the U.S. military focuses on how to effectively manage and utilize specific military electromagnetic frequency bands under intense electronic warfare conditions, specifically how to maintain unimpeded access and use of the electromagnetic spectrum to meet military needs, rather than organizing and conducting electromagnetic spectrum operations. Therefore, the ‘electromagnetic spectrum’ cannot be defined as an independent operational domain.Secondly, due to the vast differences in operational tempo, styles, and capabilities within different ‘domains’, their temporal and spatial characteristics also vary significantly — in time, ground special forces may engage the enemy at a speed of around 5 km/h, while a naval carrier strike group can cruise at speeds of up to 30 knots, air combat F-22s can fly at a supersonic speed of Mach 2.25, and satellites in the space battlefield orbit at a first cosmic velocity of 7.9 km/s. In space, in the future ‘Multi-Domain Operations’, the weapon systems of military powers have far exceeded the limits of regional geographical space in terms of strike rate, precision, and range, from the surface of the ocean to the depths of the ocean, from highlands on land to the atmosphere and outer space, and from terrain features that affect operations in small areas to the ‘curvature of the Earth’ that influences long-range precision strikes, the entire Earth and even parts of the space environment may become military spaces.To help commanders better understand the ‘multi-domain integration’ in terms of time and space, the U.S. military’s ‘Multi-Domain Operations’ concept proposes two cognitive tools: ‘Operational Framework’ and ‘Temporal Elements’. As shown in Figure 2, in terms of time, the ‘Multi-Domain Operations’ concept proposes five temporal elements: ‘preparation time, planning and execution time, duration, reset time, and cycle time’, where preparation time refers to the time needed to create conditions for employing a certain capability; planning and execution time refers to the time for maneuvering and applying influence to a target; duration refers to the time required to achieve the desired effect using a certain capability; reset time refers to the time needed to regenerate sufficient capability between two deployments; and cycle time refers to the iterative time from planning to reset. Some time elements closely related to physical effects (e.g., ballistic missile attack time) can be accurately predicted, while others related to cognition (e.g., the duration of effects from public opinion guidance in cyberspace) can only be roughly estimated based on specific situations.10In terms of space, the ‘Multi-Domain Operations’ concept introduces the ‘Operational Framework’ as a visual cognitive tool, based on physical space, to organize and integrate various operational elements distributed across different times and spaces, dividing the ‘multi-domain battlefield’ into ‘deep fire areas, deep maneuver areas, near areas, and support areas’, allowing joint forces to better integrate cross-domain, cross-environment, and cross-functional physical, virtual, and cognitive capabilities, to discover, open, and exploit ‘windows of advantage’11, achieving freedom of maneuver for joint forces in a denied environment.12
Figure 2: ‘Multi-Domain Integration’ in the U.S. Military’s ‘Multi-Domain Operations’ Concept
Conclusion
Rigorous conceptual definitions are the logical starting point for academic research. When interpreting U.S. military documents, attention should be paid to the differences in defense language systems, adhering to a historical perspective to meticulously examine the connotations and extensions of military terminology, striving to base interpretations of U.S. military frontier operational theories on authoritative official documents, rich and detailed materials, and accurate and idiomatic translations, while avoiding ‘mirror thinking’, especially refraining from generalizing and interpreting another party’s concepts using one’s own discourse system. In the study of ‘Multi-Domain Operations’, seemingly simple terms such as ‘domain’ are merely the ‘tip of the iceberg’, and may involve many complex issues behind them. International military studies require rigorous academic reasoning rather than assumptions. [1]Army Training and Doctrine Command, United States Army White Paper, Multi-Domain Battle: Combined Arms for the 21st Century, Oct 2016, p.6.[2]Army Training and Doctrine Command, Version 1.0, Multi-Domain Battle: Evolution of Combined Arms for the 21st Century 2025-2040, Oct 2017[3]Army Training and Doctrine Command, Version 1.5, Pamphlet 525-3-1, The US Army in Multi-Domain Operations 2028, Dec 2018[4]Small Wars Journal. Hoffman, F. G. & Davies, M. C. “Joint Force 2020 and the Human Domain: Time for a New Conceptual Framework?” http://smallwarsjournal.com/jrnl/art/joint-force-2020-and-the-human-domado-time-for-a-new-conceptual-framework June, 2013[5]Joint Chiefs of Staff, Joint Vision 2020. June, 2000. P. 6.[6]Over The Horizon, Tom Flounders, Multi-Domain Thinking and the Human Domain, [EB/OD] https://ot-hjournal.com/2017/07/03/md-thinking-human-domain/, July, 2017[7]Zhang, Zhanjun, “The Emergence and Development of Joint Operations”, Military Studies, 2012, Issue 6.[8]Department of Defense, Dictionary of Military and Associated Terms, February 2019, p.122，[9]Department of Defense, JP3-13.1, Electronic Warfare, 8 February 2012[10]Army Training and Doctrine Command, Version 1.0, Multi-Domain Battle: Evolution of Combined Arms for the 21st Century 2025-2040, October 2017, p.26.[11]Window of Advantage refers to the integration and concentration of various operational capabilities within a defined time, space, and specific operational domain or environment, helping commanders seize local control and create a physical, virtual, and cognitive advantage, thereby creating favorable conditions for U.S. joint forces to maneuver. The window of advantage transcends simple comparisons of resources between adversaries, emphasizing decisive strikes against the enemy’s critical points at critical nodes of warfare to establish an ‘immediate winning advantage.’[12]In the U.S. military’s concept, maneuver refers to the use of forces through the combination of movement and firepower to create a positional advantage over the enemy, thereby accomplishing missions, which can be divided into operational maneuver, tactical maneuver, and close combat types. In this sense, maneuver also carries the meaning of ‘combat.’
