Russia invested enormous political capital and material resources in the Crimean or Kerch Strait bridge. After the July 17, 2023 attack that sheared a road span and killed civilians, Moscow moved quickly to replace spans and restore traffic, presenting the repairs as proof of resilience and control. However, the operational fixes that reopened lanes in late 2023 did not eliminate the bridge’s asymmetric vulnerabilities to unmanned surface vehicles and other maritime drones.

Three technical realities explain why. First, surface and small semi-submersible USVs built for kamikaze missions are inherently hard to detect and stop at distance. Recent Ukrainian designs operate very close to the waterline, use low-signature materials and small thermal signatures, and can be launched from beyond visual range. In January and early 2024, video and field reports credited MAGURA-class and other USVs with striking Russian naval vessels and ports, demonstrating the vessels’ lethality and reach. Those operational successes underscore that small radar cross-section, shallow draft and low acoustic signature make maritime drones difficult to spot until they are already within weapons engagement zones.

Second, the sections repaired after the July 2023 attack addressed above-water road and rail spans far faster than they could fully harden or re-engineer the underwater foundations and approaches. Repair campaigns focused on replacing damaged spans, installing temporary supports and restoring traffic lanes on an urgent timeline. Those measures reduce immediate disruption but do not fundamentally negate avenues of attack that target piers, piled foundations or the bridge’s marine approaches. Repairing superstructure is necessary for reopening traffic, but it is an imperfect substitute for comprehensive maritime protection.

Third, maritime drones offer operational options that match the bridge’s geometry. The Kerch Strait is long and exposed along both approaches. An uncrewed surface vessel that can approach a pier, deliver an explosive charge at or below the waterline, or detonate against a span can exploit the same hydrodynamic leverage that sank or disabled ships during recent Black Sea operations. The attacks on Russian patrol ships and larger surface units in 2024 show that paired and swarming USV attacks are not theoretical. They have been used to strike hulls and propulsion areas, and the same tactics can be adapted against fixed infrastructure where a precise contact or shallow underwater blast can compromise a support.

Moscow’s immediate countermeasures have reduced some risk but cannot eliminate it. Russian authorities have layered responses: intensified patrols, coastal radar and optical surveillance, localized booms and physical barriers, and placement of blockships or obstacles in choke points to force attackers into more exposed approaches. These measures raise the cost and complexity of an attack, but they also impose predictable chokepoints where determined operators can mass assets or exploit gaps at night and in adverse weather. Historical precedent and open-source analysis suggest boom defenses and buoyed barriers improve protection near ports and narrow straits, but they are blunt instruments against semi-submersible craft or well-networked swarms.

From an engineering perspective the most dangerous attack vectors are at or below the waterline. Above-deck repairs can be visible and rapid. Detecting and protecting piles, pile caps and submerged connections requires underwater inspection, sonar coverage and counter-UUV capabilities that are more complicated and slower to scale than plugging a damaged roadway. Maritime drones that can operate under, along or very near the water surface therefore retain options to damage load-bearing elements even after visible repairs are complete. Technical literature on unmanned underwater and surface systems highlights detection challenges and the particular threat to subsea infrastructure.

Strategically, the continued USV threat changes calculus in three ways. First, logistics: even if the bridge can be repaired rapidly after strikes, recurring attacks force Russia to maintain redundant supply routes, divert convoys, or accept increased transit times and risk, which complicates operational sustainment in southern theaters. Second, symbolism and deterrence: attacks on such a highly political prize impose psychological and reputational costs that are asymmetrical to the resources required by attackers. Third, escalation management: maritime drones occupy a grey zone between tactical strikes and strategic escalation. They provide plausible deniability and can be used selectively to impose costs without crossing thresholds that would invite overwhelming response. That ambiguity makes them attractive in protracted campaigns but also hard for third parties to regulate.

Policy and technical implications follow. For Russia, the only durable mitigation strategy is a layered defense built for small, low-signature threats rather than solely for conventional naval platforms. That means dense, short-range radar and electro-optical coverage coordinated with sonar and active acoustic nets, hardening of underwater structural elements, prepositioned intercept assets, and the capability to deny staging areas along approaches. For Ukraine and other actors developing USV capabilities, the lesson is that asymmetric maritime tools can remain operationally relevant so long as countermeasures are costly to deploy and gaps can be found in coastal defenses. For third parties and global infrastructure owners, Kerch is a warning: long bridges and exposed maritime connectors anywhere are at growing risk from relatively low-cost unmanned systems.

Looking ahead, expect both offense and defense to iterate. Attackers will continue to refine endurance, guidance and low-observability while defenders will invest in detection, rapid interception and selective hardening. The end state is unlikely to be absolute security for any single bridge. Instead, the persistent contest will raise the cost of using that crossing for large-scale logistics and compel actors to treat critical maritime infrastructure as contested spaces in peacetime and in conflict. In that strategic environment, repairs are necessary but not sufficient. Durable protection requires sustained investment in maritime domain awareness, underwater engineering resilience and the political will to accept the operational tradeoffs that come with defending long, exposed links over water.