Sergei Eshchenko / Reuters Greenpeace activist Anthony Perrett of Britain looks out from a defendants' box at a district court in Murmansk, Russia, on Sept. 29, 2013

Greenpeace could not have chosen a worse time to set sail for the Russian Arctic. On Sept. 15, as the eco-activists were making their way into the Barents Sea, Russia’s main news networks were trumpeting the return of the Russian military to the northern frontier. Admiral Vladimir Korolyov, commander of the Northern Fleet, was shown on state-run television raising the Russian tricolor over a permanent military base in the Arctic, the first one Russia has opened since the fall of the Soviet Union. “We shall consider these flags to be raised here forever,” the admiral said. “This is our territory, and we shall defend it.” Three days later, Greenpeace arrived, intending to stage a protest against Arctic oil drilling. Instead they stumbled into Russia’s show of force.

For the first time in history, Russia’s entire fleet of nuclear-powered ships, led by the guided-missile cruiser Peter the Great, had been dispatched to the region. Like the military air base they had come to unveil, the flotilla’s mission was to warn away Russia’s rivals in the Arctic, primarily the U.S., Denmark, Finland, Norway and Canada. As it happened, several of the activists on the Greenpeace vessel were citizens of these very countries, while the captain of the ship, Peter Henry Willcox, is an American. So their stunt gave Russia just the opportunity it needed to underscore the message of Admiral Korolyov: Do not tread on the Russian north.

On Sept. 19, when the Greenpeace ship arrived to hang an antidrilling banner on a Russian oil rig, that message was delivered by the coast-guard forces of the FSB, the post-Soviet successor to the KGB. Ordering the Greenpeace ship to halt, the FSB began firing warning shots, first from their Kalashnikov assault rifles, then from their artillery cannons. A group of FSB agents then dropped down onto the vessel from helicopters and arrested at gunpoint all 28 activists and two journalists onboard. On Oct. 2, the admiral’s message was hammered home by Russian prosecutors, who began bringing charges of piracy against the activists. If convicted, they face up to 15 years in prison.

Vladimir Chuprov, head of the Arctic program at Greenpeace Russia, admits that the timing of the mission, coming in the middle of the nuclear flotilla’s historic patrol of the Russian north, may have been inopportune. “These [military] movements may have changed the way our mission was perceived, both in the eyes of the media and the security services,” he tells TIME. A year ago, Chuprov points out, Greenpeace staged a similar protest on exactly the same oil platform, Prirazlomnoye, which belongs to Russia’s state-controlled energy giant Gazprom. Greenpeace activists even chained themselves to the rig during last year’s protest and refused to climb down. “That time we were even more forceful, and the border guards did not react at all,” says Chuprov. Indeed, no charges were filed last year against the Greenpeace activists.

But last year, the scramble for control of the Arctic had not yet reached its current pitch. In 2014, the U.N. will receive competing claims on Arctic territory from all of the Arctic nations, and as Russia made clear in 2007, when its explorers planted the Russian flag on the seabed beneath the North Pole, it wants the lion’s share of the Arctic, as well as the seas of oil and gas beneath it. So the appearance of Greenpeace activists was seen by many in Moscow as a threat to these intentions, especially since the protest took place one week before President Vladimir Putin addressed a conference on Arctic policy in the far-northern city of Salekhard. “Russia’s leaders live in a world of conspiracy theories,” says Alexander Golts, an independent military expert in Moscow. “None of them have any doubt that all of these so-called activists work on the orders of the U.S. State Department, the CIA and so on.”

In light of the timing of the Arctic protest, Kremlin hawks and military brass would therefore have seen it as an act of foreign aggression, meant to spoil the mood of Putin’s Arctic summit last month while also pushing back against Russia’s military buildup in the north. “So these activists are being used to send a signal,” says Golts. “‘Stay away, don’t mess with the way we do things on our territory.’”

On Sept. 25, when Putin addressed the Arctic summit in Salekhard, the activists did get some hope of avoiding lengthy prison terms. Asked about their fate, Putin told the conference, “It’s completely obvious that of course they are not pirates.” But it was also obvious, Putin said, that “these people violated the norms of international law and got dangerously close to the [oil-drilling] platform.” He even added that the activists “tried to seize” the rig. So for now, the so-called Arctic 30 remain in detention in and around the far-northern city of Murmansk. But whatever sentences they receive, their voyage will already be a lesson to Russia’s Arctic enemies, both real and imagined.