The United States, President Trump has declared, must seize control of Greenland from Denmark because Denmark cannot defend the territory from an invasion by Russia or China. The obvious problem with this argument is that Denmark is a member of NATO, and Article 5 of the NATO treaty obliges every other NATO power—the United States included—to defend Greenland if it is attacked. But let us set aside this fact and examine the practicalities of Russia or China invading Greenland in the first place.

An old saying in military academies holds that amateurs think strategy, while professionals think logistics—and an invasion of Greenland would be a logistical nightmare. Unlike Ukraine, Greenland is an island and therefore inaccessible by cross-border roads or railways. It is also remote, freezing cold, barely inhabited, and large—about four times the size of France and three times the size of Texas. About eighty percent of the territory sits under ice between one and three kilometres thick. On the island itself, only about 383 kilometres (238 miles) of local roads exist in a handful of scattered settlements, most of which are just villages. There are no roads connecting one settlement to another. You either fly from village to village, or you sail.

If the Russians are to take Greenland, they are going to have to invade by sea or air. The sea to the north and east of Greenland is icebound and white, not blue as it appears on the map, and while the Russians have nuclear icebreakers at their disposal, these are usually limited to ice three metres deep or thereabouts. A lot of the “multi-year” ice (as distinct from seasonal ice) is thicker than that and cannot be broken by icebreakers at all. The Russians could resort to snowmobiles, but ice is not always conveniently flat and putting an entire army on snowmobiles for journeys of hundreds of kilometres would be absurd. And there are no service stations on the sea ice either.

So the Russians would have to sail past Iceland to get to Nuuk, on the western side of Greenland’s tip, where the port is ice-free for most of the year. The distance from Murmansk, on Russia’s northwestern coast, to Nuuk is about 3,500 kilometres (2,200 miles)—a five or six day voyage for modern ships. Chinese invaders, on the other hand, will have to sail through the Bering Strait (between Russia’s eastern tip and Alaska) and Canadian waters to get to Greenland via the North West Passage in the Canadian archipelago, assuming it is open. Or they would have to go the long way around via the Panama Canal. At a pinch, they could take the really long way round via Cape Horn (at the southernmost tip of South America) or the Cape of Good Hope (at the southernmost tip of Africa). 

If either Russia or China invades Greenland, they face major challenges in preventing long maritime supply lines from being cut. At present, the Russian navy is struggling to survive attacks by Ukrainian boat drones. A few submarines and planes could make life very difficult for Russian or Chinese supply convoys. Besides the US, several NATO powers have submarines, and the British and the French both have nuclear-powered attack submarines armed with nuclear missiles, which could sink a supply convoy. The Dutch, the Norwegians, the Swedes, the Spanish, the Germans, the Greeks, and the Turks all have conventional submarines. The Danes do not, but they do have F-35s. So do the United Kingdom, Norway, the Netherlands, Italy, and Poland. Even Belgium has F-35s. The British and French have three aircraft carriers between them. In total, non-US NATO has around 180 destroyers and frigates, some seventy submarines, and around 1,300 aircraft with anti-ship capabilities. So there is plenty of non-US air and naval power to resist a Russian or Chinese attempt to take Greenland by force.

These sobering naval obstacles make an air invasion more attractive, at least at first blush. In theory, the Russians could simply fly 2,200 miles over the Arctic ice and drop airborne units into Nuuk, and into Pituffik on the island’s northwest coast, where the United States maintains a Space Force base. In practice, it is vanishingly unlikely that the Russians are going to attempt to take a US base anywhere—particularly a base with an early-warning system intended to identify Russian missiles travelling across the Arctic. The US would intercept Russian planes long before they got anywhere near Pituffik. And even if the Russians were able to capture a US base in Greenland (there is only one), they would certainly not be able to hold it.