A number of Ukrainian military units have been involved in the strikes against Crimea. For the 9th Kairos Battalion of the 414th Unmanned Systems Brigade, planning for the campaign to cut off the peninsula began in the spring and was conceived as three phases.

First came the attacks against land routes on and into the peninsula, then strikes on large stockpiles. The third phase, focused on sea lanes, began last week, when it became clear that the Russian vessels were exposed and vulnerable, said Fin, a senior sergeant in the brigade. He gave only his call sign in keeping with military protocol.

To reach the Sea of Azov, Ukrainian soldiers have to pilot their drones roughly 250 miles, navigating Russian air defenses and electronic warfare. Over the sea, Sergeant Fin said, they fly just above the waterline to evade radar and hit their targets.

There is no indication that Ukraine’s Crimea campaign has swayed Moscow. The Kremlin has expressed defiance, unleashing punishing ballistic missile strikes on the Ukrainian capital, Kyiv, and vowing to press forward in its efforts to capture more territory in eastern Ukraine.

But the Russian foreign minister, Sergey V. Lavrov, condemned the attacks, calling them worse than piracy. And Russian pro-war commentators and bloggers have angrily accused Russia’s top brass of failing to protect vessels in the sea.

Voenny Osvedomitel, one influential blogger, urged action and struck a pessimistic note.

“If things keep going this way, we are going to end up with a Strait of Hormuz of our own, where Ukraine will play Iran and we’ll be the U.S.,” he wrote on Telegram. “Our ships simply won’t be able to get to Crimea and back unharmed by the drones.”

Reporting was contributed by Jenny Gross, Oleg Matsnev, Aric Toler, Daria Mitiuk, Nataliia Novosolova and Sanjana Varghese.