When I was a kid, I loved Legos and Transformers. They could take multiple shapes and let me play out a million different adventures from the same set of building blocks and plastic robot heroes and villains. Why can’t I have that versatility as an adult in my arsenal of democracy?
The answer is a flawed measure of effectiveness in modern weapon systems that focuses on single mission performance instead of fungibility and able to conduct multiple missions with the same piece of kit.
In the wake of the recent NATO summit, the alliance needs to look forward and ask itself what can strengthen collective defense over the coming decades. At the same time, the alliance will have to do more with less as the costs of aging populations crowd out the ability to surge defense spending. In other words, even though defense spending is rising to combat authoritarian states like Russia and China, there are structural limits to these increases due to the need to finance social safety nets and healthcare systems. This dilemma calls for new thinking about collective defense.
Given these challenges, the future of NATO’s military power — and with it the credibility of the alliance — rests on complementing its historic focus on interoperable forces with a new interest in fungibility. Fungibility — a core economic concept — implies that a military capability can be deployed on multiple platforms and used to conduct multiple missions, thereby lowering opportunity costs without losing its contribution to military power. Fungible systems may be more expensive to buy but are cheaper in terms of the range of missions they can accomplish. This makes them more adaptable and more valuable. Just as fungible financial assets preserve economic value, fungible military assets enable a more flexible force capable of accomplishing a wider range of missions. As a result, a more uncertain and high-risk threat environment puts a premium on fielding fungible military forces.
From Interoperability to Fungibility
A hidden hallmark of the NATO alliance has been its commitment to interoperability. It is one thing to have a collective defense pact. It is another to ensure 32 countries have military forces that can fight alongside one another.
The alliance defines interoperability in broad terms to include anything that better connects member states along technical, procedural, human, and informational lines. Technical interoperability ensures that hardware and armaments have standard measures. Procedural and human interoperability deals with doctrine, tactics, and establishment of a common terminology and training to ensure allies have a shared understanding. Information interoperability includes efforts to build a connected battle network that bridges, for example, NATO’s federated mission networking with the mission partner environment for U.S. allies connected to the combined joint all-domain command-and-control network. It is what drives the need to build deeper interoperability and embrace data science, AI, and machine learning as seen, for example, in ongoing experiments run by the Pentagon’s Chief Digital and Artificial Intelligence Office.
Interoperability is constantly in the making. It requires time and resources at both the state and alliance level, ranging from exchanges to war games and exercise programs. For NATO’s Allied Command Transformation, interoperability is the capstone concept in its exercise program and the hackathons it co-sponsors with member states.
NATO understands what it takes to fight as an interoperable force, even if it struggles at times to achieve it. But now it needs to start thinking in terms of fungibility as well.
As I wrote earlier, fungibility is an economic concept referring to the extent to which a good is interchangeable for another good without a significant loss in value. The goods might be different (i.e., commodities, currencies), but the value is similar. This property produces multiple benefits including easing the exchange of goods and assets in a manner that leads to more efficient markets, optimized risk management, and better returns.
Outside of economics, fungibility played a role in helping scholars in the 1990s analyze if states could substitute military power for political power alongside the utility of force. Scholars like David Baldwin held that military force was fungible but highly contextual. The fungibility of power varies from situation to situation, making some instruments of power subject to diminishing marginal returns when incorrectly applied.
What has received less attention is a more operational analysis of fungible military concepts and capabilities. Can any piece of equipment — from artillery to a fighter jet — conduct multiple missions without a significant loss in value? To the extent that one piece of equipment can, it should produce — consistent with the theory of fungibility — ease of exchange, increased efficiency, and optimized risk management. When a fifth-generation fighter paired with collaborative combat aircraft can perform both counter-air missions and close air support, it provides more options to commanders (ease of exchange) while also allowing them to optimize the expected payoff from changing mission conditions. The same is true of ground combat. If a towed howitzer can provide fire support and contribute to air defense, it is fungible.
This implies two types of fungibility. Platform fungibility describes how a single weapons platform — for example, an MQ-9 unmanned aerial vehicle or a vertical launch cell on an unmanned surface combatant — can use multiple types of weapons. Mission fungibility defines a situation in which a single munition or class of munitions can be adapted to increase its optionality. The missile that can kill tanks, small ships, and — more often in practice — unsuspecting terrorists (i.e., high-value individual targeting) is fungible across missions. While both forms of fungibility are desirable force-design attributes, the ideal is to have both: a multi-mission capable platform that can fire weapons and hold multiple targets at risk.
There are historical precedents. The Flak 36 multipurpose gun developed by the Germans in the interwar period was an effective anti-air and anti-tank weapon that could even be fired from submarines. Since its introduction in the 1980s, Hellfire missiles have gone through multiple iterations that allow the air-to-ground missile to be fired at small naval ships, employed by light ground vehicles, and even fired from surface combatants like the littoral combat ship.
The two concept and capability mixes discussed below illustrate the promise of embracing fungibility as a core force design attribute.
Fungible Guns
It is now possible to field old-fashioned guns capable of both mission and platform fungibility. First, standard artillery shells can be adapted to become cannon-based air defense. By generating an electrical current in flight and powering data links, shells become mission fungible. They can be used to augment short-range air defenses, making them direct and indirect fire weapons usually thought of in terms of infantry-support capable of engaging drones and cruise missiles.
This concept grows out of experiments as part of the third offset to use high-velocity projectiles fired from howitzers to intercept everything from cruise to ballistic missiles. The concept also found traction in Japan, which experimented with a mix of high-velocity projectiles and data-linked artillery to engage cruise missiles and drone swarms.
What has changed is that new approaches focus more on data networking than intercept speed. It is better to shoot a slow arrow and hit the target than miss with a Mach 5 missile. This approach lowers the cost and makes weapons ranging from the 30mm cannons standard on infantry fighting vehicles to towed and/or mobile 155mm howitzers fungible.
Second, old-fashioned guns can take on new missions based on platform fungibility. The Mojave — an unmanned aircraft originally built for supporting ground forces — can be equipped with air-to-air missiles and gun pods to conduct defensive counter-air missions against slower moving targets like loitering munitions, subsonic cruise missiles, and helicopters. This concept is on display as Ukraine mobilizes slow flying prop planes to defend against loitering missiles. To increase their survivability, the unmanned aircraft could be paired with another aircraft using electronic warfare and jamming to obscure enemy air defense targeting. This system, currently being employed by the U.S. Marine Corps, makes even slow flying unmanned aircraft difficult to target. This combination of sensors, air, and ground-based air defense creates a mobile and flexible air defense in depth. It won’t stop fourth- and fifth-generation jets, but it will deny cruise missiles, loitering munitions, and helicopters. The fungibility of the gun achieves new reach when paired with a network that enables smaller, flexible air–ground teams to protect the forward edge of the battlefield from barrages of cruise missiles, loitering munitions, and drone swarms.
In addition, fungibility allows units to rapidly transition from defensive counter-air to suppression of enemy air defense and interdiction along the forward edge of the battlefield at machine speed. Imagine the Mojave unmanned aircraft providing targeting support for 3D-printed, air-launched effects swarming alongside loitering munitions fired from unmanned ground vehicles and even remotely piloted helicopters to attack Russian air defenses protecting an advancing armored column. While the Mojave and unmanned helicopters are at risk from surface-to-air missiles, the use of jamming to create attack windows of opportunity can reduce their vulnerability. Regardless, platform and mission fungibility present the enemy with a dilemma.
These flexible missions will also require new approaches to data. NATO should expand formal standards for interoperability to include new concepts like the modular open systems approach to support computing-intensive tasks like sensor fusion and AI-enabled analysis. This concept should embrace an open-source architecture to make it easier for NATO to dynamically organize large, unmanned forces. There will still be humans in the loop and even mechanics on the ground to support new battle groups, but code will be king and enable new tactics.
Fungible Missiles
Like old-fashioned artillery rounds and dumb guns, decades-old missiles can adopt new roles based on a mix of platform and mission fungibility. The Standard Missile — a class of modern missiles — is fielded on naval destroyers and ground-based AEGIS Ashore facilities. It has a proven track record of intercepting ballistic missiles, cruise missiles, aircraft at extended ranges, and naval vessels. Earlier variants of these missiles were even used in Operation Burnt Frost to shoot down a U.S. satellite and demonstrate America’s counter-space capability. New standardized containers like the MK 70 Mod 1 payload delivery system add to the missile’s fungibility. The containers allow the missile to be fired from land, including the U.S. Army’s new truck mobile Typhoon launcher, and smaller naval vessels like the littoral combat ship and future optionally manned surface vessels, adding platform fungibility to this family of missiles’ mission fungibility. Recent experiments have confirmed the ability to fire the missile from fighter aircraft, increasing the standoff range. This mix of platforms and missions helped the U.S. Navy develop new warfighting concepts including distributed lethality and its successor, distributed maritime operations. In short, fungibility generates options.
These options can be expanded through increased interoperability between partners and allies. Japan has deployed the Standard Missile on its destroyers for years. Australia fields the weapon in its new surface combatants, including the Hobart-class destroyer. The Netherlands is in the process of buying the Standard Missile for its new class of frigates. South Korea is procuring them for its AEGIS destroyers to support ballistic missile defense.
The fungibility of the Standard Missile enables planners to consider a wider range of contingencies for confronting emerging threats. Imagine a near future scenario in which Russia uses military power in the Mediterranean to threaten NATO with a combination of anti-access/area denial bastion coastal defense, advanced air defenses, fighter squadrons, and a reinforced Mediterranean Fleet that includes submarines stationed in Tartus. The combined effects allow Russia to hold naval and air assets at risk over large portions of the Eastern Mediterranean.
In developing its flexible response options, NATO planners can tailor different approaches because of the fungibility of the Standard Missile. A standing NATO maritime group could operate alongside a U.S. Army multi-domain task force to support an enhanced integrated air and missile defense as a demonstration of capability to Russia during a crisis. This conventional deterrent signal would be strengthened by the fact that Russian forces would know that Standard Missiles could be used in both an anti-air and anti-ship role. In the event of a transition to limited hostilities, the NATO Maritime Group could pull back and use F/A-18s to fire Standard Missiles to attack Russian frigates. All of these missions could in turn grow in effectiveness when tied into a battle network based on the modular open systems approach and using unmanned aircraft targeting over-the-horizon threats with signals intelligence.
Conclusion
If interoperability defined efforts to generate combat power across the NATO alliance during the Cold War, fungibility should guide collective defense in the 21st century. Fungibility does not replace interoperability. It complements the concept and creates a theory of advantage based on freedom of action and optionality.
A new network of authoritarian states has the political will and resources to challenge what is left of the international order. That will bring more conflict, not less, to Europe’s doorstep and could even see free societies pulled into far-flung wars around the globe. The only way to meet the challenge is through building credible combat forces. That credibility underlies deterrence and the ability to fight wars beneath the nuclear threshold. Modern credibility rests on fielding interoperable and fungible forces that can pivot between missions and enable more dynamic task organization, optimizing forces in response to threat scenarios in a way that creates options and tempo. This adaptability provides new avenues for confronting mass since, sadly, authoritarian states seem primed to outproduce free countries regardless of the cost it imposes on their own citizens.
Like the Cold War quest for interoperability, fungibility will require experimentation and investments in people. NATO should use a mix of its schools, task forces, and battle groups to encourage bottom-up concept development, including testing new formations in head-to-head simulated combat via networks like Fight Club. The best concepts to emerge could be tested in an iterative manner to enable rapid prototyping and fielding. Done right, this process will create a culture of experimentation and produce entirely new types of units better aligned to the realities of modern combat.
Benjamin Jensen, Ph.D. is the Petersen Chair and a professor of strategic studies at the School of Advanced Warfighting in the Marine Corps University as well as a senior fellow in the Futures Lab at the Center for Strategic and International Studies. He is also an officer in the U.S. Army Reserve. The views expressed are strictly his own and not indicative of any official government or industry position.
Image: Royal Air Force
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