BRUSSELS—Wars in Ukraine and the Middle East are forcing NATO to rethink how it would counter a Russian attack—including by taking off the gloves and striking far inside Russian territory.

Top officers and officials from across the North Atlantic Treaty Organization gathered in June for the alliance’s first-ever Deep Strike Symposium. Hosted by U.S. Air Force Gen. Alexus Grynkewich, NATO’s top military commander, the discussions and wargame tackled a topic few attendees would have openly addressed until recently.

Protecting NATO’s European territory for decades centered on the military equivalent of putting up roadblocks. But after almost five years of Moscow’s war in Ukraine, NATO strategists say a Russian invasion won’t be thwarted by merely impeding an advance.

Deterring the Kremlin’s conventional forces now requires more active prevention or, in military speak, denial. That entails not just blasting troops that might pour across borders, but also hitting military bases, supply depots and industrial facilities behind the front line, on Russia’s home ground.

Grynkewich recently spelled out the approach in a speech on his “theory of victory,” explaining that NATO’s defensive forces would first block the initial wave of any attack and then blunt follow-on action. If the offensive were to continue, he told a Warsaw audience, “we will break the warfighting system engaged against us” by hitting both advancing forces and “anything and everything that supports, sustains, or controls that force.”Escalating to nuclear weapons isn’t in the strategy.

Central to the plan is highly precise deep-strike weaponry—both high-end and less expensive. The U.S. has recently been upgrading and extending its array of precision deep-strike missiles, including Tomahawk cruise missiles and Atacms rockets, while developing new systems. European allies, who have lagged behind, are racing to field new models and boost their small stocks of Storm Shadow, Scalp and Taurus cruise missiles.

Across Europe, at least 48 new low-cost cruise-missile projects involving 20 manufacturers have been announced, according to Fabian Hoffmann, a senior researcher at the Norwegian Institute for Defense Studies who specializes in missiles. When any of those will deliver arms is an open question. Many won’t materialize, and even those that progress will need years.

Definitions of “deep” vary from around 100 miles to hundreds of miles, but broadly refer to targets far behind the front line.

In combat, long-range missiles, rockets and drones would be used to pick off not only traditional military targets at great distances—like remote air fields or army compounds—but also Russia’s industrial facilities, critical infrastructure and resource bases that lie thousands of miles from NATO borders.

The approach—often described as hitting an archer, rather than shielding from arrows—is one that Ukraine has taken against Russia. Using increasingly powerful weapons, including the domestically developed Flamingo cruise missiles, Kyiv has struck distant Russian military and economic assets, such as rocket-fuel producers, drone-battery plants, oil refineries and data centers. It is also an approach the U.S. deployed against Iran this year.

Russia, meanwhile, has launched a much larger number of long-range strikes on Ukraine, mixing pinpoint attacks on strategic targets with widespread destruction of civilian assets. Ukraine has run short of Western-supplied interceptors to protect itself, so is relying increasingly on deep-strike “proactive defense” to hit Russia, said Ukraine’s ambassador to NATO, Alyona Getmanchuk.

“Air defense is like a painkiller—it can alleviate the symptoms—but you need to target the source of the pain,” Getmanchuk told a conference on Ukrainian defense.

A crucial lesson for NATO from Ukraine is that “defense also means striking back,” and precision deep-strike attacks are a crucial part of that, said Polish Maj. Gen. Ireneusz Nowak in an interview. “We definitely would want to strike the defense-industrial base” in a fight with Russia, he said.

“We need to treat deep precision strike as deterrence,” Nowak said, noting that if Ukraine had it early in the war, fighting wouldn’t have “resulted in trench battles like in World War I.” While military leaders across NATO now accept “denial” as doctrine, many strategists wonder if European politicians would stomach a deep-strike response to a Russian incursion.

“There is a disconnect between the military planning that is reasonable to defend against Russia—which definitely includes offensive components—and the political decision makers, who believe defense is just putting up a wall or readying a drone wall,” said Nico Lange, a former chief of staff in Germany’s Defense Ministry.

Military plans like Grynkewich’s aim to make deep-strike attacks essentially automatic following a Russian military attack. They also aim to clarify why stockpiling the weapons is necessary.

Ukraine has shown that large supplies of precision weapons are vital because new targets continually emerge as conflicts wears on. Fixed assets like factories are relatively straightforward to target, but they may be relocated to several, hidden locations—as Ukraine has done. Mobile targets like launchers, meanwhile, can be even harder to strike because they are small and continually reposition.

“What we’ve seen is that you don’t want to be caught in a high-intensity conflict where your adversary has access to deep arsenals of long-range strike capabilities and not have them yourself,” said Hoffmann.

Deep-strike attacks date back to World War II, when both sides relied on manned bombers. One U.S. bombing mission hit Nazi-controlled oil fields far inside Romania. Germany deployed the world’s first targeted long-range military rockets, the V1 and V2, which it rained on Britain and infrastructure including the Belgian port of Antwerp, an Allied supply node after D-Day. None of those methods was reliably precise.

During the Cold War, ballistic missiles grew more accurate but were big and complex to fire. Deep precision strike made a dramatic debut during the first Gulf War in 1991, when the U.S. fired hundreds of Tomahawks. They flew horizontally, using small jet engines, rather than rockets like ballistic missiles.

Since then, the U.S., its allies and adversaries have expanded cruise-missile arsenals, developed precision rockets like Atacms fired from U.S. Himars trucks, and recently blurred the lines between drones and missiles.

NATO commanders say that to prepare for conflict—and hopefully deter it—they must quickly build out their deep-strike arsenals.

“The message needs to be: Don’t do anything stupid, because we can punish you,” said Poland’s Nowak. “But to be credible, we need to have those capabilities.”