According to the U.K. Ministry of Defense intelligence update on Aug. 9, the Russian merchant tanker Sig was "attacked and disabled near the Kerch Strait" on Aug. 4 by a sea drone, or Uncrewed Surface Vessel (USV).
The night before, a Russian Navy landing craft stationed in Novorossiysk was damaged in a similar attack.
CNN and several Ukrainian media outlets cited sources in Ukraine's security service who said that the attack on the Olenegorskiy Gornyak on Aug. 4 was the result of a joint operation between the Security Service of Ukraine (SBU) and the Ukrainian Navy.
The U.K. Defense Ministry said that the attack was a "significant blow to the Black Sea Fleet" and "represents the largest Russian naval vessel seriously damaged" since last April, when Ukraine sunk the cruiser Moskva.
According to the intelligence update, attacks using sea drones "are increasingly a major component of modern naval warfare and can be turned against the weakest links of Russia’s sea supply lanes."
Unlike the Olenegorskiy Gornyak, the Russian merchant tanker is technically a civilian vessel. However, the U.K. Defense Ministry said that it has long been contracted to transport fuel and military supplies from Russia to Syria.
The ship became critical for supplying Syria since the start of Russia's full-scale invasion of Ukraine. Since February 2022, Russian military ships are not permitted to pass through the Bosphorus and into the Mediterranean.
The intelligence update added that two days before the attack on the Sig, the Russian navy allegedly prevented a similar attack on patrol boats that were escorting Russian merchant vessel Sparta IV, which also transports supplies for the Russian military to Syria.
The Kyiv Independent's source in the Defense Ministry confirmed that Ukrainian military intelligence conducted a naval drone attack on Russian patrol ships in the Black Sea, 340 kilometers (211 miles) southwest of occupied Sevastopol, overnight on Aug. 1.