Ukraine's military may not be able to retake Crimea, but it can make life hell for Russians there, experts say

• Ukraine is gearing up for what's expected to be a counteroffensive against Russian forces.
• There's debate inside and outside of Ukraine about whether and how Kyiv can recapture Crimea.

Rather than a costly ground offensive to liberate Crimea from Russian control, there may be an easier way: Use unmanned boats to attack Russian forces and blockade the peninsula, argue two American experts.

Ukraine does not "need to drive occupying forces out of Crimea to render it less hospitable to Russia's purposes," William Courtney and Scott Savitz, two researchers at the RAND Corporation think tank, wrote in an essay published by The Moscow Times in April.

Defending the Crimean Peninsula, which Russia invaded and annexed in 2014, has historically presented a quandary. A land invasion from the northwest — the direct route — must cross the narrow and easily defended Perekop isthmus between the peninsula and the mainland.

On the other hand, a hostile army can just as easily block communications between Crimea and the mainland. This would force Russia to supply the peninsula either by sea or by road and rail using the 11-mile Kerch Strait bridge on the eastern side of the peninsula, which connects Crimea with the Taman peninsula in southern Russia.

In October, a Ukrainian truck bomb badly damaged the bridge, which Ukrainian officials recently said they would target as part of the counteroffensive.

The result is that Russia's ability to supply and reinforce its military in Crimea — or retreat, if need be — by land depends on two precarious chokepoints.

"The geography that makes Crimea hard to invade facilitates a modern-day siege," Courtney and Savitz wrote. "All Russian movements by land must pass through one of two constrained corridors. The first entails traversing hundreds of miles of occupied territory, including areas relatively close to the front and crawling with hostile populations, saboteurs, and special forces. The final gauntlet is the isthmus, a target-rich place with minimal room for maneuver and within range of current Ukrainian weapons."

That leaves the Black Sea route. Ideally, Ukraine would either launch an amphibious invasion of the peninsula — as Britain and France did in the Crimean War in 1854 — or starve out the Russians through a naval blockade.

But the Ukrainian navy is much too weak to take on Russia's Black Sea Fleet, which lost its flagship but still fields about six diesel-electric submarines as well as several dozen missile-armed frigates, corvettes, patrol craft, and other support vessels.

But Ukraine could use unmanned surface vessels laden with explosives to damage and destroy Russian ships. Ukraine has already employed USVs to damage Russian warships and to attack the Russian naval base at Sevastopol, at the southern tip of the Crimean peninsula.

"USVs are well-suited for networked swarm attacks, and relatively low-cost," Courtney and Savitz wrote. "Their nascent designs can be modified to make them stealthier and harder to detect than most crewed vessels. Sinking a warship in a confined channel could create obstacles that would take weeks to clear, or longer if under fire."

If sea and land links to Crimea are blocked, that would only leave air transport. Supplying Russian forces on the peninsula — including the Black Sea Fleet — would require far more airlift capacity than Russia has. "Ukraine could attenuate this flow by targeting runways and fuel facilities on the peninsula," they wrote.

"Augmented by other weapons, Ukrainian forces could hinder Russian forces from using it as a safe haven from which to attack the mainland or threaten Black Sea shipping," Courtney and Savitz added. "Rattled by attacks, short of supplies, and somewhat isolated, Russian forces in Crimea could become less capable."

A naval drone blockade has its risks. Ukrainian aerial drones and GPS-guided weapons such as HIMARS rockets are already being hampered by Russian jamming. It is possible that Russia could devise some defense or countermeasure against USVs, especially if they have naval and air superiority over the Black Sea.

Perhaps the biggest drawback to a drone blockade is the time it would take. Siege warfare has always been slow and painstaking. Sapping the capabilities and morale of Russian forces by disrupting their supply lines is one thing. If the ultimate goal is to liberate Crimea and force the Russians out — as Ukrainian officials have repeatedly vowed to do — that may require a ground offensive.

But Ukrainians and Russians can both read a map. The obvious Ukrainian strategy is to drive eastward across southern Ukraine and the Black Sea coast, cutting off the neck of the peninsula. The obvious Russian strategy is to defend that area, and in fact Russian forces have built multiple fortified lines meant to thwart attacks by land or sea.

That is a recipe for a bloodbath, but blockading Crimea with robot attack boats may be a way around it.

Michael Peck is a defense writer whose work has appeared in Forbes, Defense News, Foreign Policy magazine, and other publications. He holds a master's in political science. Follow him on Twitter and LinkedIn.