Drone boats give Ukraine a cheap, 'asymmetric' edge against Russia and may have just damaged a key bridge

• Waterborne drones are an inexpensive asset, giving Ukraine an "asymmetric" naval edge against Russia.
• Russia blamed Ukraine for using the drones to attack the Kerch Strait Bridge in Crimea on Monday.

Ukraine has heavily relied on cheap-but-effective airborne drones for attacks on front-line Russian positions and on targets behind enemy lines. Waterborne drones are also inexpensive and devastating, and there are indications they were used to damage a key Russian bridge into Crimea.

On Monday, explosions rocked the 12-mile Kerch Strait Bridge, damaging the roadbed, halting traffic, and killing two adults. Russian authorities blamed Kyiv, vowing "targeted and quite inhumane" repercussions.

It's at least the second time the bridge has been damaged in less than year. Last October, a bomb-laden truck exploded, severely damaging the bridge and killing three people. It was closed to normal vehicle traffic until February 2023 and railway traffic until May 2023.

Russian state media attributed Monday's incident to Ukraine's unmanned drones, and Ukrainian state media outlet, Ukrinform, citing sources in the Security Service of Ukraine, said the SBU and Kyiv's naval forces carried out the nighttime attack and that unmanned surface vessels were involved.

An anonymous source from Ukraine's Security Service also confirmed to CNN that Ukraine's naval drones carried out the attack, as did a state official.

In general, unmanned surface vehicles (USVs) — commonly called drone boats — are remotely operated waterborne vessels. There's been a push to develop waterborne drones for both Ukraine and the US, the latter increasing production to counter China while the former looks for ways to counter Russia's formidable military.

Ukraine has been crowdfunding the development of a full-blown naval drone fleet, noting that the unmanned vessels first gave them an operational advantage to target Russian ships in October 2022. "The killers of Ukrainian civilians — warships armed with missiles — became targets themselves," a state-run fundraiser said.

They can pack a punch, and they're relatively cheap, too, especially compared to a traditional warship or the defenses required to defeat these unmanned surface vessels.

"The cost of manufacturing and fielding these vehicles is considerably less — many magnitudes less — than the cost of trying to defend against them and just basic resource allocation in trying to interdict and destroy these assets," said Samuel Bendett, a research analyst with the Center for Naval Analyses' Russia Studies Program.

"So again, the cost of defending against such vehicles falls on the defender — a single ship, a fleet, or an entire country — while the cost of manufacturing them is considerably smaller."

The result is an "asymmetric advantage" for Ukraine. They stress Russian defenses at a low cost to the Ukrainians and their available resources.

The Kerch Bridge, which may have been the target of these assets, is a valuable access point for Moscow, connecting Russia to Crimea and allowing economic and cultural control over the illegally occupied territory.

It also served as an ideal transportation route for Russia's military equipment before its February 2022 invasion. Supply routes have mostly shifted to northern land bridges since October's attack, according to Bendett, but the repeated incidents raise a host of questions about how Russia is going to defend the Kerch Bridge.

"These USVs don't travel for thousands of kilometers, they have to operate in relative proximity to their operators or their launching point," Bendett said. "How do you defend a long bridge like that? Where do you place your defenses? Do you fly patrols around it? Do you install sensors on it all the time? Do you have maritime patrols all the time?"

In short: "It's difficult to properly and completely defend an asset as large as a bridge like that."

And although it's too early to tell how significant Monday's attack on the bridge is and what the impacts will be, especially since only part of the roadbed was damaged, Kyiv can, assuming its forces were the ones who executed the attack, can presumably count this as a win.

"Ukraine exploited its [the Kerch Strait Bridge] vulnerability by launching relatively cheap and inexpensive USVs in what turned out to be a successful attack," Bendett said.