NATO's promise of collective security rests on the notion that aggression against one member of the Atlantic Alliance triggers a response from all. Yet Russia's swift, stealthy operation to annex Crimea and destabilize eastern Ukraine has cast doubt on the Alliance's capacity to fulfill that promise. What can NATO realistically do if Vladimir Putin sets his sights on the Baltic states?

 The latest warning comes in a report last week by the Defense Committee of the U.K. House of Commons. The report surveys NATO's widening conventional capability gap with Russia, highlights the Kremlin's aggressive nuclear posture and points to the doctrinal limitations that could hamstring the Alliance's response to the next round of aggression.

Its stark conclusion: "NATO is currently not well-prepared for a Russian threat against a NATO Member State." Case in point: The British Army now fields a grand total of 156 main battle tanks, amounting to a single regiment. Russia has more than 2,800 active main battle tanks, according to a 2013 study by the International Institute for Strategic Studies.
The committee notes that the Kremlin has unveiled an ambitious plan to expand and modernize Russia's conventional forces, with the aim to increase the proportion of conventional assets classed as "modern" to 70% by 2020, up from 10% in 2012.

Then there is Russia's bold nuclear-force posture. "Russia sees its strategic nuclear forces as a key deterrent to potential Western intervention or belated response to Russian aggression," the committee notes. "Russia dedicates a third of its Defense budget to them." Moscow has at least twice since 2009 simulated nuclear strikes, including one targeting Warsaw. By contrast, the Obama Administration earlier this year announced plans for sharp, and unilateral, cuts to the U.S. strategic force well ahead of the 2018 deadline set by the New Start treaty.

 The committee's most important findings relate to outdated doctrines that could prevent the Alliance from keeping pace with Moscow's sophisticated, evolving strategy. A linchpin of Russian strategy is what the committee calls "ambiguous warfare." As one Russian defense theorist puts it, ambiguous warfare involves using irregular forces, cyberattacks and information warfare to "neutralize adversary actions without resorting to weapons (through indirect actions), by exercising information superiority."

 The trouble ambiguous warfare poses to NATO is that the Alliance's collective-defense obligations, and the strategic doctrines pinned to them, call for responding to "armed" assaults. But Russian aggression against, say, Lithuania may not look like an outright assault. The Kremlin is more likely to use Russian-language media to agitate the country's ethnic-Russian population while debilitating basic state functions through cyberattacks and the deployment of irregular commandos.

 The Crimean operation provided a blueprint for such attacks, and the Atlantic Alliance would be foolish not to update its doctrines to meet the new Russian threat when the next NATO summit convenes in Cardiff in September. But no amount of doctrinal evolution will matter if NATO members continue to treat national defense as a minor concern.