When NATO leaders gathered in Lisbon in 1952, the Alliance hoped to have 50 divisions available to deter Soviet attack. By the end of the Cold War it had over 100. At the end of June, with war raging in Ukraine and a revanchist Russia making nuclear threats towards its members, NATO’s leaders gathered a short distance away in Madrid with just eight forward-deployed battlegroups at their disposal.

In Madrid NATO revealed its new strategic concept and made significant force posture changes to bolster deterrence and defense. These measures were described by Secretary General Jens Stoltenberg, as “the biggest overhaul of our collective deterrence and defence since the Cold War.” However, although the concept sets out a high level of ambition, NATO still has plenty of work to do to meet it. While the threat from Russia has returned to Cold War levels, NATO’s strategy is playing catch up. To close the gap, NATO should revitalize — and modernize — the basic tenets of the “sword and shield” strategy and the “hedgehog defense” that contained Soviet aggression.BECOME A MEMBER

The Sources of NATO’s Conduct

To judge NATO’s eighth strategic concept it helps to understand the previous seven. NATO’s approach to its fundamental task of deterrence evolved throughout the Cold War and was transformed after it. Its first two strategic concepts — formalized in 1949 and 1952 — were designed to deter by punishment and denial. The threat of nuclear punishment relied on the advantage conferred by U.S. strategic nuclear forces, which compensated for the numerical superiority of Soviet conventional forces. This was complemented by the plan of General Dwight Eisenhower — then Supreme Allied Commander Europe — for NATO to “make itself into a hedgehog of defence.” This involved both forward defense to “arrest the enemy advance as far to the East as possible,” and active opposition to peacetime aggression through “all measures short of war.”

To counter growing Soviet conventional and nuclear forces, NATO leaned more heavily on nuclear deterrence in its 1957 concept, adopting the doctrine of “massive retaliation” — which included the possibility of nuclear first use in response to conventional Soviet aggression. This was replaced in 1968 with “flexible response,” designed to provide a range of conventional and nuclear options to boost deterrence credibility short of nuclear response. This basic strategy of balancing nuclear and conventional deterrence through its “sword and shield” saw NATO through the rest of the Cold War, helping deter and contain Soviet expansionism.

Back to the Future

After 1989, NATO sought to build a more constructive relationship with Russia while managing key risks through dialogue and arms control, moving away from the sword and shield towards a smaller “balanced force mix.” This shift was captured in NATO’s three post-Cold War strategic concepts. But Russia’s 2014 annexation of Crimea and instigation of conflict in the Donbas region fatally undermined NATO’s new approach. As a result, the 2014 Wales summit declaration reset relations with Russia, putting partnership on ice and bringing deterrence back to the fore. NATO increased defense spending, established a new high-readiness response force and returned to its forward presence roots — albeit at a much smaller scale than the Cold War shield forces — with four battlegroup-sized missions in the Baltic states and Poland. Recognizing the renewed salience of measures short of war, NATO also added non-military cyber and hybrid threats to its Article 5 collective defense guarantee for the first time.

Putin’s invasion of Ukraine on Feb. 24, 2022 sealed the fate of NATO’s post-Cold War strategy. In response, the new concept unveiled in Madrid returned Russia to its Cold War status of adversary, describing it as “the most significant and direct threat to Allies’ security and to peace and stability in the Euro-Atlantic area.” It also committed to “significantly strengthen deterrence and defence for all Allies.” To deliver the new concept, Stoltenberg declared a “fundamental shift to our deterrence and defence” based on three pillars: more forward-deployed combat units, more prepositioned equipment, and more high-readiness reinforcement forces.

A Point of Departure

Yet Madrid was not the revolution many of NATO’s eastern allies were hoping for. Rather than a transformative shift to a credible forward defense, NATO’s new posture will look to some like a slightly thicker tripwire. As U.K. Defense Secretary Ben Wallace admitted before the summit: “[The eastern allies] won the argument that the tripwire strategy was not really up to what we have seen happen in Ukraine. The first fight is the most important fight.” Yet it seems unlikely those allies will be satisfied for long that NATO’s new posture will give them a substantially better chance at winning the first fight for their homelands than they had before the summit. As one Estonian official put it: “We need to move to deterrence by denial. We need a credible military construct on the Eastern flank that will deter Putin.”

Fortunately, Madrid was a point of departure for NATO, not the final destination. Even if some allies remain underwhelmed, the strategic concept sets a new level of ambition and gives NATO political headroom to strengthen its posture over time. The concept returns NATO’s nuclear sword to the fore — “reaffirming the unique and distinct role of nuclear deterrence” — and brings back the shield, moving away from a forward-presence tripwire to “deter and defend forward with robust in-place, multi-domain, combat-ready forces.” The shift towards deterrence by denial is not just about territorial defense — it also updates and broadens the concept for the modern strategic environment, confirming that hybrid, cyber, or attacks in space could “invoke Article 5 of the North Atlantic Treaty.”

To meet this new level of ambition, NATO allies should follow up the concept over the coming months with three initiatives inspired by its Cold War strategy: sharpen the sword, strengthen the shield, and bring back the hedgehog. This means making NATO’s nuclear posture more credible, investing in forward defense with conventional forces, and boosting the resilience of Eastern allies to deter and resist all forms of Russian aggression.

Sharpen the Sword

First up, NATO should sharpen its nuclear sword through modernization, signaling, and doctrine. NATO’s nuclear posture — based on the strategic nuclear forces of the United States, United Kingdom, and France, and incorporating non-nuclear allies through nuclear sharing arrangements — remains its most potent deterrent. Yet the credibility of NATO’s nuclear deterrent is being undermined by Russian modernization and nuclear signaling.

First, modernization. According to NATO, Russia has modernized most of its strategic nuclear forces over the past two decades, while developing new delivery systems. These include hypersonic missiles and novel technologies like the unmanned nuclear torpedo. Russia also has many more non-strategic nuclear weapons in the region:1,500 compared to around 100 U.S. B-61 gravity bombs. These weapons fall outside the New START treaty, which was extended last year until 2026. To make sure the balance of terror continues to hold, NATO allies should fully support U.S. efforts to modernize its nuclear triad and update their nuclear sharing capabilities.

The second challenge is nuclear signaling. From the outset of his invasion Vladimir Putin has used nuclear threats to deter NATO from intervening. Although concerning and irresponsible, this is to be expected according to Russian doctrine. As Michael Kofman and Anya Loukianova Fink point out, “Russia’s strategy of deterrence by fear-inducement when under military threat makes heavy use of nuclear signaling, which serves to create the impression that the country is far looser with its thinking on nuclear use than is actually the case.” This playbook includes threats to vital infrastructure. As ex-president Dmitry Medvedev put it: “Accidents can happen at European nuclear plants too.” Nuclear scholar Kristin Ven Bruusgaard has argued Russia’s nuclear strategy is related to its conventional inferiority. The key question now is therefore whether heavy losses in Ukraine will lead Moscow to become more reckless with its own nuclear saber — to both manage escalation in Ukraine, and deter NATO intervention.

The dilemma for NATO is the same one it faced during the Cold War: Western reluctance to use nuclear weapons gives Russia leverage to both risk conventional attack and threaten nuclear use without fear of reprisal. This gap could be closed by updating NATO doctrine with a new “flexible response” . In the Cold War this doctrine filled the gap between conventional defense and massive retaliation by adding the intermediate option of “deliberate escalation” through non-nuclear force or selective nuclear strikes. Adopting a similar policy today could be done without lowering NATO’s threshold for nuclear use — a move that may divide allies and undermine cohesion.

A new flexible response could emphasize and enhance the threat of a conventional response to Russian escalation (for example, attacks against arms depots in Poland or Romania, which become more likely as the war in Ukraine drags on). This threat would rely primarily on America’s global strike complex and its capacity for aerospace attack, which have generated real fear in Russia. This strategy would be a form of “hands off the wheel” brinksmanship based on the likelihood of any high-intensity NATO-Russia exchange escalating to the nuclear realm. It is a risky gambit given the inherent uncertainty of escalation dynamics. But it may be preferable to the alternatives of ceding Moscow coercive advantage or lowering NATO’s own nuclear-use threshold.

Strengthen the Shield

Any sharpening of NATO’s nuclear sword will also require its forward defense shield of conventional forces to be strengthened. Just as Russia’s conventional and nuclear strategies are linked, so are NATO’s. During the Cold War the alliance made up for reliance on massive retaliation by developing a large, forward-deployed shield force to deter conventional attack. As U.S. General Lauris D. Norstad, then Supreme Allied Commander Europe, explained in 1961:

“The substantial dependence which we must place on nuclear weapons is reflected in our plans; nevertheless, as conventional capabilities improve or increase, it should clearly be possible, under certain conditions, to raise the level of involvement at which such weapons would have to be introduced into the battle.”

The credibility of the deterrent provided by NATO’s shield forces during the Cold War was a product of their size and scale. It is true that while Putin’s threatening rhetoric towards NATO is reminiscent of the Cold War, the physical threat from Russia’s armed forces is not. In 1987, the balance of forces in central Europe favored the Warsaw Pact nations, who had 69 forward-deployed divisions and over 20,000 tanks, compared to NATO’s 37 divisions and nearly 10,000 tanks. Today, with up to 80,000 casualties it may be true that “Russia’s performance so far in Ukraine suggests that the balance of power in Europe is less daunting for NATO than previously thought.”

Still, it would be unwise to discount the threat from Russia to eastern Europe. Putin has already declared his hand: He has unfinished business to right “the greatest geopolitical catastrophe of the century,” the collapse of the Soviet Union. Given the lengths he has gone to in Ukraine, it is understandable that many in ex-Soviet nations with significant ethnic Russian populations fear they might be next. As Lithuania’s Chief of Defence, Lieutenant General Valdemaras Rupsys, put it: “After some time … they will try to threaten us by military means. You will see.” It may therefore be prudent for NATO’s military planners, as they did during the Cold War, to plan against Russia’s “maximum intentions.”

Now that they have established a clear level of ambition, NATO should seize the moment and deploy credible forward-based shield forces that give its members more confidence they won’t be wiped off the map. They should start by meeting their Madrid commitment to scale up “existing battlegroups to brigade-size units where and when required.” In this case the “where” should be the three Baltic states and Poland, and the “when” should be as soon as physically possible. Just as after 2014, these four nations remain the most vulnerable in NATO to Russian aggression. The British-led presence in Estonia is the closest to meeting this goal, with two battlegroups deployed. Allies should not stop at brigades, but work towards combat-ready divisions in all four nations — something the Baltic states requested prior to Madrid. The U.S. commitment to permanently deploy its Army’s V Corps headquarters in Poland can provide the basis for generating and commanding larger-scale formations there, while the United Kingdom has already committed practical support to develop “a divisional-level command structure in Estonia.”

How much is enough? Beyond the forces already deployed since the war began, Brookings fellow Michael O’Hanlon suggests that 15,000 U.S. troops in the Baltics and Poland, matched by European and Canadian allies, “is an affordable and prudent response to the increased Russian threat to NATO’s forward regions.” This would move NATO’s presence towards the 1:3 ratio of local defending to attacking forces that holds some credence among military analysts. A focus on the Baltics and Poland is also prudent due to their lack of strategic depth: Home-based reinforcements would count for less here (and more elsewhere). A U.S. heavy division in Poland would also have the benefit of being able to “train as it fights” with Polish and other allied forces, facilitating and encouraging the development of indigenous divisions while deterring Russia with its presence.

Scaling up NATO’s forward-deployed forces in the East will not be easy: if it were, NATO would have already done so in Madrid. In the United States, there has been broad bipartisan and public support for several significant packages of military assistance to Ukraine and the redeployment of over 20,000 U.S. troops to Europe. But the latest Taiwan crisis demonstrates the pressing need for the United States to focus on China, which may preclude more U.S. force presence in Europe. European forces could fill the gap, yet after decades of downsizing many nations are lacking the high-end mass required to generate large land formations — let alone air and maritime components. Although Europe has made historic commitments to increase defense spending since Russia’s invasion, these will take time to yield deployable forces. There is also the additional challenge of ensuring that deployments actually reassure, rather than scare, the local population.

Bring Back the Hedgehog

Finally, NATO should bring back its “hedgehog defense.” Like the hedgehog – a peaceful creature until attacked – the Cold War concept of “active defense” held the promise of deterring attack while minimizing the security dilemma associated with force build ups. It had three elements: covering forces, designed to ambush and disrupt the lead elements of an invading army; “defense in sector,” using natural terrain to channel the advance and attrite enemy forces; and counterattack to regain lost territory and target rear echelon forces. This concept later evolved from “linear” towards “maneuver” defense, exploiting new technology and doctrine (including the U.S. “AirLand Battle” concept). NATO military planners should update active defense from first principles, accounting for Russia’s own active defense concept. Several initial ideas are worth considering.

One idea for developing covering forces is “confidence building defense,” a late Cold War concept that balances between deterrence and provocation. It advocates a “spider in the web” of dispersed, highly mobile assets, with the option of quickly scaling up through prepositioned equipment and logistics. These could include the anti-tank weapons, portable drones, and artillery that have been exploited by Ukrainian armed forces for defense and counterattack. A recent study by the Center for Strategic and Budgetary Assessments suggests modern guided rockets, artillery, and mortar systems (G-RAMM) could “significantly expand the geographic areas where Russian forces could face lethal threats like those they experienced in northern Ukraine.” Going further, the authors advocate a Baltic “mini A2/AD” strategy to overturn Russia’s offensive advantage of proximity by impeding access through G-RAMMs and short- and long-range air defense systems.

Long range precision strike would also enable targeting in depth in support of counterattacks, although their expense may require larger allies to provide or field them. A cheaper option may be the so-called “stay behind forces” developed by NATO during the Cold War using special forces and non-military clandestine units. To this end, an Atlantic Council report calls for expanding U.S. and European special operations forces activities, while the Center for Strategic and Budgetary Assessment authors recommend establishing a new NATO Special Warfare Centre of Excellence in Estonia. More broadly, they argue a new NATO operational concept for “follow-on forces attack” could contribute “significantly” to deterring Russia.

Such a concept should include what Eisenhower called, the “very considerable sea and air power” possessed by NATO allies. In the air domain NATO should upgrade its existing air policing mission into an integrated air and missile defense mission. The air defense mission would require increasing the capacity of the multinational force that runs the NATO air policing missions in the Baltic states, Poland, Romania, and Hungary, while updating pilots’ rules of engagement in anticipation of a more assertive Russian posture. However, the bulk of air contributions to active defense should be based in Western Europe to enhance survivability for counterattack missions. The missile defense mission would require deploying more medium- and long-range air defense systems to the region — for example increasing the number of Patriot or National Advanced Surface-to-Air Missile systems deployed to Poland and the Baltics. Integration could be achieved through the existing framework of NATO’s Integrated Air and Missile Defence System.

As for the contribution of NATO’s maritime forces, one study advocates increasing the number of Standing NATO Maritime Groups from two to five to bolster NATO’s ability to patrol and secure its territorial waters, from the Baltic Sea to the Black Sea. The constant presence of the U.K.-led Joint Expeditionary Force in the Baltic Sea also adds another layer of deterrence and should be enhanced — especially now that its headquarters has been deployed to the region. NATO’s maritime defense in the Baltic Sea region will also benefit from the addition of Finland and Sweden to the alliance. Maritime forces can also render NATO’s counterattack ability more potent through precision strike munitions launched from above and below the surface.

The final element in a new hedgehog defense for NATO is to deter so-called hybrid threats below the threshold of armed attack. These have been described as the modern Fulda Gap, or Russia’s most likely axis of attack. As NATO’s new concept points out, threats have proliferated in kind across space and cyberspace to encompass “the coercive use of political, economic, energy, information and other hybrid tactics.” Although a military alliance, NATO’s resources go far beyond conventional military capabilities, including sophisticated capabilities in strategic communicationsinformation operationscyber defenseoffensive cyber, and counter-hybrid warfare teams. Here NATO would benefit from closer coordination with the European Union and the European Centre of Excellence for Countering Hybrid Threats based in Helsinki to spread best practice in Cold War style “total defense,” particularly as Finland and Sweden both excel in this department. Last month, Estonia’s largest ever military exercise showed how their reserve forces could operate with forces from ten NATO allies to put total defense into action. Its name? Exercise Hedgehog.

Just as during the Cold War, NATO’s challenge will increasingly be to deter all forms of aggression at once: sub-threshold, conventional, and nuclear. To meet the level of ambition agreed in its new strategic concept, NATO should revitalize deterrence by sharpening its sword, boosting its shield and bringing back its hedgehog defense. Madrid was an important point of departure for NATO, but the alliance’s journey toward stronger defense and deterrence has only just begun.