The building was once an abattoir — and it smells that way. Inside the grey, peeling structure, men in dark tracksuits pull down their facemasks to smoke cigarettes. Upstairs, someone has taped old bed sheets over the broken windows.

Outside, a helicopter flies low overhead. A purple, red, and yellow flag — which rebel forces have tied to a pole and wedged into a rotting woodpile — twists around itself. The flag looks a lot like la tricolor of Spanish Republicans.

Approaching the complex on a woodchip-covered road in eastern Lithuania, I'm told that for the purposes of today, I should imagine the derelict building is a working radio station. Then, I should imagine the radio station has been seized by separatist insurgents, backed and armed by a fictional enemy state called Udija. The rebel commander of Udija is inside; it is from here that he has been orchestrating a string of hybrid insurgent attacks across central and eastern Lithuania.

In a few hours — around lunchtime, when the rebels' spirit seems to be flagging, and some of the insurgents start checking their cellphones — a handful of armored personnel vehicles will appear, letting out bands of camouflage-covered soldiers who will snake towards the radio station and lob gas grenades through the windows, so that the masked men inside cough and lose their footing. Fire will be exchanged for over an hour — and the sound of blanks firing will delight the cluster of little boys who have gathered along the road to watch the Udijan separatists be vanquished by Lithuanian soldiers.

Photo by Henry Langston/VICE News.

In the end, several dozen rebels will be left to play dead: on the ground, limbs akimbo, with wounds made of plastic, glue, and fake crimson blood on prominent display.

And so passed one morning of Operation Lightning Bolt: a four-day simulation exercise carried out last week by the small Baltic state of Lithuania — because Lithuanian leaders fear that the Russians are coming, just as they came before for Ukraine.

Throughout the drill, however, none of Lithuania's army commanders would mention Russia by name. Instead, they spoke of the fictional land of Udija — or sometimes "the East."

VICE News embedded with the Lithuanian Army for four days as it carried out its first ever nationwide test of the country's 2,500-strong "Rapid Reaction Force" (RRF), set up in the wake of the Ukraine crisis to deal with the sort of plots that typify conflict in the region — armed protests, airfield and weapons stockpile seizures, the sudden appearance of "little green men" who seem to take orders from far away. "One thing is clear now," Lithuanian Brig. Gen. Vilmatas Tamosaitis, told the New York Times soon after plans to build an RRF were announced: "We have to be ready. We have the same neighbors that Ukraine does."

In March, Lithuanian president Dalia Grybauskaite told the BBC that her country was "already under attack." In September, she called Russia a state with "terrorist elements".

Across the region, forces are being mobilized to pre-emptively thwart Russian military meddling. Last week, US tanks rolled through the Estonian countryside, a mere 65 miles from the Russian border, as part of the 13,000 troop Operation Steadfast Javelin. And the Nordic Sea played host to the curiously titled Operation Dynamic Mongoose.

But Lithuania, an EU and NATO member state, has been most hawkish in its stance against the East. The RRF — formed of two battalion-sized groups, with corresponding logistics, special operation troops, and air support — is the first of its kind along NATO's eastern border.

On the evening that the drill began, I visited the General Adolfas Ramanauskas Warfare Training Center in Nemencine: a town outside the Lithuanian capital of Vilnius of scattered forests and architecturally ambitious, if rather unsightly, suburban-style homes. There, I met Major Arnas Mikaila, who led me into war games HQ: a desk-lined room with an enormous, floor-sized map of Lithuania. Under flickering yellow lights, a man in army fatigues was moving cardboard pyramids — of various colors, representing various military and civilian units — from one side of the floor to the other.

The premise of Operation Lightning Bolt, Major Mikaila explained, was of an unconventional sort, from an army standpoint. The drill did not assume that a foreign nation had breached Lithuanian territory, in such a way that would trigger Article 5 of NATO's Washington Treaty — "The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all"_ — _and so suck in allied forces from across the continent. Rather, the drill envisioned a peacetime scenario, in which shadowy rebels from inside the country were the primary antagonists— carrying out the kind of unrest that, were it not backed by a foreign enemy, would be dealt with by civilian police.

As the major spoke, the drill was beginning. Lithuanian troops were being deployed from their barracks, police were beginning to blockade cities, and borders were being placed on lock down.

Back in December, the Lithuanian government laid the ground for this exercise, when it adopted the Statute on the Use of the Armed Force, allowing for the deployment of armed national troops in "peacetime." In an interview with local journalists in March, Major General Jonas Vytautas Zukas said the primary lesson he learned from Ukraine was that national forces must be able to crush aggression immediately, even before martial law was formally declared.

Walking atop the map, Mikaila points out strategic locations with a long, silver walking stick. He gestures towards the fictional land of Udija, which occupies the real-life territory of Kaliningrad Oblast: a Russian exclave wedged between Lithuania and Poland on the Baltic Sea — just a three-hour drive from Vilnius — which houses Russia's Baltic fleet and which has, in the last year, been flooded with Russian arms and personnel.

In December, Russia carried out a snap military drill in Kaliningrad with some 9,000 soldiers, 642 military vehicles, 100 artillery units, and 55 warships. In April, Lithuanian foreign minister Linas Linkevicius said Moscow was pouring "all sorts of weapons" into the region, including short-range Iskander ballistic missiles.

So what do these Udija-backed separatists want? "According to intelligence information," said Mikaila, "criminal groups have become a resistance front to fight for the independence of East Lithuania."

Back outside the abattoir building, I ask the soldiers-come-rebels about Udija's leader. Does he have a name? Yes. He is President Anton LaPat.

And why do people support him? "They say he will bring the order, re-establish some old values."

And does LaPat happen to have a penchant for posing topless in photographs? The men snicker.

Photo by Henry Langston/VICE News.

That Lithuania is preparing for Russian encroachment is no great surprise, and not just because of Ukraine. Russian leaders argue that ethnic Russians are routinely suppressed by Baltic governments — and last September, Russia's foreign minister warned that this "discrimination" may have "far-reaching, unfortunate consequences."

In April, at a closed-door meeting with an American official in Germany, a Kremlin delegation reportedly argued that "the same conditions that existed in Ukraine and caused Russia to take action there" were also present in Lithuania, Latvia, and Estonia.

Earlier this month, the head of Lithuania's National Security Committee announced that Russian spies had been attempting to make contact with their former, Soviet-era colleagues — old KGB agents living in Lithuania. Around the same time, Lithuanian authorities arrested a Russian citizen who allegedly sought to "penetrate" Lithuanian law enforcement and intelligence agencies.

In turn, Lithuania has announced plans to increase military spending by some 50 percent, to around $456 million, and to buy a cache of equipment from German armed forces_,_ including 12 tanks. It is also providing lethal aid to Ukraine.

In February, the government announced it would reintroduce conscription across the country. Around the same time, the Lithuanian Defense Ministry published a 98-page guide, "How to Act in Extreme Situations or Instances of War," which advises citizens on what to do in the event of blockade, or disinformation campaign, or cyber-attack, or the sudden appearance of armed soldiers who wear no insignia and who claim to be without government affiliation. "Keep a sound mind, don't panic and don't lose clear thinking," explains the manual. "Gunshots just outside your window are not the end of the world."

That Lithuania would be outright flattened if Russia's military directly took on its 8,000 soldiers is beyond obvious. And indeed, parts of Operation Lightning Bolt drew attention to chronic military deficiencies. At one exercise on May 10, a pretend airfield was dotted with ageing armed personnel carriers and second-hand, castaway Land Rovers.

But NATO has similarly been readying its members for trouble along its eastern edge. This year, the Alliance agreed to expand its own rapid response force from 13,000 to 30,000 troops — and last year agreed to establish a "Very High Readiness Joint Task Force," which will be capable of deploying in 48 hours. NATO will also open six new Eastern European commander centers, in Poland, Bulgaria, Romania, Estonia, Latvia, and Lithuania. The United States is reportedly providing intelligence support to the force — heightening the sense that NATO is coalescing around its post-WWII raison d'etre: to stand guard against Moscow.

In this way, the specter of Russian aggression has, in part, altered the trajectory of Europe's military development — as NATO member states rush to bulk up old-school ground forces that can skip quickly across large swaths of territory.

Should Russia invade, the RRF is meant, in the words of one general, to "buy some time until NATO can get here." But for the most part, Lithuania's RRF is turned inwards — readying for possible Moscow-backed insurgencies from within.

Some Lithuanian officials believe that this separatist lurch might begin on television. In April, Lithuania's media regulator kicked the Russian-language station RTR Planeta off the air for allegedly pushing Kremlin propaganda: it was "inciting discord, warmongering, spreading biased information." Lithuania's military reportedly lobbied for the ban.

This — and the upcoming restart of national conscription — may explain why Lithuanian armed forces are bending over backwards to win the good will of ordinary Lithuanians. Indeed, civilian charm offensives were built into Operation Lightning Bolt. After one military exercise in the town of Kaisiadorys, soldiers set up a kind of town fair, in which civilians could get a taste of Lithuanian military rations (bowls of oily porridge with lumps of ground beef) and play around with military equipment. Women in teetering heels posed for photos with rocket launchers and children climbed through the interior of polished Armored Personnel Carriers.

Yet noticeably, throughout the drill, the troops demurred when I asked a fairly fundamental question: Would Russia really do it? What would Moscow gain from invading Lithuania? With a Russian population of just 6 percent, Lithuania lacks the sizeable ethnic Russian populations that both Estonia and Latvia have (more than a quarter of the population in each case) — and thus plays less into Putin's Russian-speaking pan-Slavic vision.

But Aleksandras Matonis, a defense analyst in Vilnius, said the lesson from Ukraine is that "either you feed your own soldiers or you need to feed foreign forces." Also, fend for yourself. "Either you believe in NATO or you don't," he told VICE News. "I choose to believe. [But in] Afghanistan, we saw that some NATO allies do not fulfil their obligations… It's difficult to rely only on allied unity."

Photos by Henry Langston/VICE News

You don't have to spend much time in Lithuania for the conversation to shift back in time — to earlier years spent in Russia's shadow. In 1940, Lithuania was annexed by the Soviet Union — only to have Nazi German troops enter a year later, rout the Soviets, and begin the killing of nearly 200,000 Lithuanian Jews. In 1944, the Germans retreated and the Red Army reoccupied the country, this time, deporting hundreds of thousands of people — and kicking off a years-long partisan guerrilla war, which saw tens of thousands killed and many more wind up in Siberian gulags. Only in 1990 did Lithuania become the first Soviet Republic to declare independence.

The story of Lithuania's double Soviet occupation is often used as a modern-day rallying cry.

In the middle of the forest near Kaisiadorys, during one Operation Lightning Bolt drill, Major Linas Pakutka told me that this history has made Lithuanians less susceptible to Russian propaganda. "That's why I think we are more loyal than Ukrainian forces are," he said, over a salty lunch of shredded, boiled beetroot, and inky pork sausages.

But other soldiers at the table worried that Udijan President Anton LaPat and his fifth column Lithuanian associates might interpret history somewhat differently. "They say [Udija] will bring order, re-establish old values," said one officer. "They feel nostalgia for the old times."