Ukraine claimed it carried out an underwater drone strike on Dec. 15, the first such attack in maritime warfare, that critically damaged a Russian Kilo-class attack submarine at the Russian port of Novorossiysk,

Despite the finding, the authorities have been unable to fix the damage from a drone that punctured Reactor No. 4’s outermost protective shield in February.

The New Safe Confinement dome protects the surrounding environment from leaking radiation, but a recent drone strike on the structure has impaired that protection.