Kerch Strait

Most chokepoints matter because the world’s trade flows through them. The Kerch Strait matters because a single country’s lifeline does. This narrow, shallow gap — between four and fifteen kilometres wide, nowhere more than about eighteen metres deep — is the only way in or out of the Sea of Azov, the shallowest sea on earth and the maritime back door to eastern Ukraine and southern Russia. Whoever holds the strait holds the Azov ports, and with them the export routes for the steel, grain, and ore of a whole industrial region. Since 2014 that “whoever” has been Russia, and the Kerch Strait has become less a trade artery than a strategic prize fought over with truck bombs and naval drones.

Geographic Position¶

The strait runs roughly 41 kilometres between the Kerch Peninsula of Crimea on the west and the Taman Peninsula of Russia’s Krasnodar region on the east, connecting the Sea of Azov in the north to the Black Sea in the south. It narrows to as little as four kilometres, and its shallowness — a navigable channel that must be dredged and maintained — funnels all traffic into a thin, controllable lane. The Sea of Azov beyond it averages just seven metres deep, which means the vessels that can use it are modest in size to begin with.

The defining structure is the Crimean Bridge, the roughly nineteen-kilometre road-and-rail crossing whose road span Vladimir Putin opened by driving a truck across it in May 2018, with the rail line following in 2019. The bridge is both engineering statement and strategic vulnerability: it physically binds annexed Crimea to the Russian mainland, and its clearance of around thirty-three metres also caps the size of any ship that can reach the Azov ports beyond — a constraint on trade quite apart from any deliberate blockade.

A Gateway, Not a Highway¶

The Kerch Strait belongs to a particular class of chokepoint — the gateway to an enclosed sea rather than a link in a global trade route. Its significance is regional but, for the region, total. The Ukrainian Azov ports of Mariupol and Berdyansk were the outlets for the country’s industrial east: steel accounted for roughly two-thirds of Mariupol’s seaborne exports, followed by iron ore, grain, and sunflower oil. After Russia’s 2014 annexation of Crimea gave it the western shore of the strait, traffic through those ports fell sharply — Mariupol’s by around 70 percent — as Russia gained the ability to slow, inspect, or halt anything bound for the Azov.

Reliable figures for current traffic barely exist, because Russia now controls both shores and operates the Sea of Azov as a closed military zone; the pre-war numbers are the last clear baseline. What can be said is that the strait’s value lies entirely in its position. Control it and you control whether eastern Ukraine has a coast at all.

The 2003 Bargain and Its Collapse¶

For a brief window, the strait was governed by agreement. A 2003 treaty between Russia and Ukraine — signed after a tense standoff that year over Russia’s construction of a dam toward Tuzla Island — declared the Sea of Azov and the Kerch Strait to be shared internal waters of the two states, open to free navigation by both. It was a workable arrangement between neighbours who, at the time, still behaved as neighbours.

The annexation of Crimea in 2014 hollowed it out. With the western shore in Russian hands, the legal fiction of shared waters gave way to the fact of Russian control, and the strait became a tool of pressure rather than a common thoroughfare. The shift turned explicit in November 2018, when Russian coast-guard vessels fired on and seized three Ukrainian Navy ships and twenty-four sailors attempting to transit toward Mariupol. The International Tribunal for the Law of the Sea ordered the sailors released; Russia returned them, but the message had landed — the strait was Russia’s to police, treaty or no treaty.

The Most Attacked Bridge in Europe¶

When Russia launched its full-scale invasion of Ukraine in February 2022, the Kerch Strait acquired a new role: logistics. The Crimean Bridge became the umbilical cord supplying Russian forces across southern Ukraine, and so it became a target. In October 2022 a truck bomb collapsed sections of the road deck and damaged the rail line. In July 2023 Ukrainian naval drones, each carrying hundreds of kilograms of explosives, struck it again. In June 2025 Ukraine’s security service detonated charges against the bridge’s underwater supports. Each time Russia repaired the damage and reopened the crossing, often within hours — but the campaign demonstrated a principle of chokepoint warfare: a piece of fixed infrastructure that an adversary cannot do without is a piece of infrastructure that can be bled.

Russia, meanwhile, has worked the strait the other way — dredging and widening the channels to the captured Azov ports and using Mariupol and Berdyansk to export grain from occupied territory, including, by Ukrainian and open-source accounts, cargoes bound for Syria, Libya, and Turkey. The figures are contested and hard to verify independently, but the pattern is clear enough: having taken the strait, Russia is monetising the sea behind it.

Asymmetric Warfare at the Bridge¶

The campaign against the Crimean Bridge has become a textbook of a new kind of chokepoint warfare. Ukraine cannot contest the strait with a surface fleet — it has barely a navy left — so it has reached instead for cheap, expendable, unmanned weapons: truck bombs, and above all the explosive-laden naval drones that its security services have developed into a genuinely novel instrument of war. A “Sea Baby” drone costing a fraction of a missile can carry hundreds of kilograms of explosives across hundreds of kilometres of sea to strike a structure that cost billions and that Russia must defend around the clock. The cost-exchange ratio runs heavily in the attacker’s favour, exactly as it does for the Houthis at Bab el-Mandeb — and the lesson generalises far beyond the Black Sea.

Russia, for its part, has poured resources into defending the bridge: booms and barriers in the water, air defences along its length, smoke screens, even barges and sunken ferries arranged to blunt drone runs. The result is a permanent siege of a fixed object — a structure too important to abandon and too exposed to fully protect. It is a vivid demonstration of why static infrastructure at a chokepoint is a strategic liability as much as an asset: the very thing that makes the bridge valuable to Russia, its indispensability, is what makes it worth attacking again and again. Every repair is also an admission that the strait can be reached.

The broader implication is that chokepoints in the drone age are more contestable than they used to be. A passage that a great power once controlled simply by holding the shore can now be harassed, and its key infrastructure threatened, by a far weaker adversary willing to spend cheap robots against expensive targets. The Kerch Strait is where that future arrived first.

Strategic Assessment¶

The Kerch Strait illustrates a kind of geopolitical leverage that the great oil chokepoints obscure. Its importance is not measured in millions of barrels a day but in the simple fact of access: it is the lock on a door, and the door belongs to a contested coastline. Control of it lets Russia treat the Sea of Azov as an internal lake, seal off Ukraine’s eastern maritime frontier, and supply the forces holding the south.

It also shows how a bridge can be both an instrument of integration and a strategic liability. Russia built the Crimean Bridge to make the annexation of Crimea permanent and tangible; in doing so it created a single, irreplaceable target whose destruction Ukraine has pursued with growing ingenuity. The strait remains, as of 2026, firmly in Russian hands, its legal status the subject of an unresolved arbitration that Russia’s conduct has rendered largely academic.

Conclusion¶

The Kerch Strait is a small body of water that has come to carry an outsized share of a continental war. It is the gateway to the Azov, the anchor of the bridge to Crimea, and one of the few chokepoints in the world where the fighting over the passage has been as literal as the fighting over the land around it. For Ukraine it is a wound — the severed access to its own eastern coast. For Russia it is a prize and a vulnerability at once: the lock it has seized, and the bridge it cannot stop defending. Whatever settlement eventually ends the war, the question of who controls these few kilometres of water will be among the hardest to resolve, because the answer decides whether eastern Ukraine faces the sea or is shut away from it.

Sources & Further Reading¶

• “The Influence of Sea Power upon History” by Alfred Thayer Mahan — the classic account of why control of narrow passages confers power disproportionate to their size.

• “Azov Sea, Kerch Strait: Evolution of Their Purported Legal Status” (Jamestown Foundation) — a detailed analysis of the 2003 treaty and how Russia’s annexation of Crimea unravelled it.

• “Carving Up Ukraine: What About the Azov Sea?” (Lieber Institute, West Point) — on the maritime-law dimensions of the conflict over the Azov and its gateway.

• “The Maritime Dimension of Russia’s War Against Ukraine” — analyses of the Black Sea and Azov theatres, including the repeated strikes on the Crimean Bridge.