Terras said that inadequate air defense capability made the Baltic region vulnerable to a Russian lightning attack. NATO needed to consider increasing the number of its warplanes based in the region, and plan for the deployment of Patriot batteries.

Seeing as Estonia’s self-defense capability was of great importance, what it also needed was air defense, Terras added. Russia’s behavior was characterized by opportunism, which is why the allies needed to be ready and look at what needed to be done now.

The NATO chiefs will discuss measures aimed at boosting Eastern European defenses at the alliance's biennial summit in Warsaw in July. As the alliance agonizes over proposals to station four battalions in Eastern Europe, concerns are growing that the measure will not be enough to provide a credible deterrent to potential Russian aggression, the Financial Times wrote.

Latvia, Lithuania and Estonia were widely seen as a prime target for Russian revanchism, should relations with NATO deteriorate further, the paper wrote. The Baltic States are linked to the rest of NATO territory by a narrow strip of land that runs between Belarus, one of Moscow's staunchest allies, and Kaliningrad, a heavily militarized Russian enclave on the coast of the Baltic Sea.

Terras said that the Baltic States could be seen as an island. The corridor connecting them to NATO territory farther southwest was small, with one railway and two roads running through it.

Basing new battalions there would be a strong first step, he added, but NATO also needed to develop its own anti-access aerial denial strategy, or A2AD, such as powerful surface-to-air missile systems. The alliance has long feared that Russia could use such systems in the region.

Russian missile systems in Kaliningrad have carved out an A2AD bubble, making it hard for the alliance to maneuver its forces anywhere in the area, even deep within its own territory. For example, it would be too risky to deploy the Spearhead rapid response force, a 5,000-strong brigade established in 2014, in most of Poland or anywhere in the Baltic region in the event of a conflict with Russia, alliance generals believe, as they would be in range of the Russian systems in Kaliningrad.

The Baltic states couldn't develop A2AD capability on their own, Terras said. They needed NATO to do so. Local troops needed to be trained to get Patriot systems deployed here quickly, and to know where to position them, if not having them based here permanently, like it was the case with Turkey, Terras added.

Any such development would provoke an angry response from the Kremlin, which has already threatened “retaliatory measures” if NATO should deploy four battalions as planned. The deployment would also up the ante in the stand-off between Russia and the U.S. over missile defense. Patriot batteries are capable of intercepting tactical ballistic missiles, but but can’t intercept intercontinental weapons.

Stepping up NATO's air power in the region could be an easier alternative, the Financial Times wrote. The existing NATO Baltic air policing arrangement involves the rotational deployment of alliance fighter jets. Four British Typhoons and four Portuguese F16s are on high alert, ready to intercept suspicious Russian aircraft. Expanding this to the scale of an air defense mission would involve a far larger deployment with combat capability.

Such decisions would be contentious, said Terras, who was confident they would be made. “The crucial thing, whatever happens, is the unity of NATO. The center of gravity for us is that unity,” he added. “Without it, we all lose.”