- Amphibious ships are used to move assault troops to land quickly, especially in enemy territory.
- Russia has also used landing ships in recent years to ferry military supplies to Syria, in support of Bashar al-Assad's government.
A big Russian amphibious ship, the Caesar Kunikov, has been sunk off the coast of Russian-occupied Crimea, according to Ukraine's armed forces.
Powerful explosions were heard early on Wednesday, according to local social media, which suggested the landing ship was hit south of the town of Yalta.
Ukraine's intelligence directorate released a video of what it said were Magura V5 sea drones striking the ship.
Ukraine has repeatedly hit Russia's Black Sea fleet in occupied Crimea.
Satellite images last year showed much of the fleet had left the peninsula for the Russian Black Sea port of Novorossiysk.
Ahead of a Nato ministerial meeting in Brussels, the secretary general of the Western defensive alliance, Jens Stoltenberg, said Ukrainian forces had won a "great victory" in recent months, inflicting "heavy losses" on the Black Sea fleet that had opened a corridor for Ukrainian grain exports.
Russia's full-scale war in Ukraine is due to enter its third year next week and Ukraine's armed forces chief has admitted the situation is "extremely complex and tense".
Col Gen Oleksandr Syrskyi, who was appointed commander-in-chief last week, visited the front line on Wednesday and promised that units trying to prevent Russian troops from capturing the flashpoint town of Avdiivka would be reinforced. Avdiivka is almost empty and all but surrounded by Russian forces and one of the soldiers defending it said earlier that the situation there was critical.
"We are doing everything possible to prevent the enemy from advancing deep into our territory," he wrote on social media.
Overnight, a Russian missile attack claimed three lives including a child in the mining town of Selydove, 40km (25 miles) west of Avdiivka. Officials said four missiles had hit the local hospital and maternity ward, as well as nine blocks of flats.
Several other residents were wounded, including a baby.
There was no confirmation from Russia's navy that the Caesar Kunikov had been sunk in the Black Sea, merely that six Ukrainian drones had been destroyed. Video appearing to show the aftermath of the Ukrainian attack was uploaded only recently, BBC Verify confirmed.
"The Caesar Kunikov suffered critical holes in its port side and began to sink," Ukraine's main intelligence directorate said on the Telegram messaging site, adding that it had been destroyed off the Crimean coastal town of Alupka in Ukrainian territorial waters by a unit called Group 13.
The Magura V5 unmanned drones it said were used in the attack are made in Ukraine and travel just above the sea surface at a speed up to 42 nautical miles an hour, their manufacturer says.
Amphibious ships are used to move assault troops to land quickly, especially in enemy territory. Russia has also used landing ships in recent years to ferry military supplies to Syria, in support of Bashar al-Assad's government.
Russian military bloggers did not deny the Caesar Kunikov had been hit, saying only that the crew had survived. Russia's military rarely reports major losses and Russians rely on a handful of popular bloggers for information.
The Caesar Kunikov dates back to the end of the Soviet era. If its sinking is confirmed, it would be the second successful strike in the Black Sea this month. A small warship, the Ivanovets, was sunk by drones in a special operation almost two weeks ago.
Another Russian landing ship, the Novocherkassk, was hit while in port in Feodosiya in December.
Russia seized and annexed the Crimean peninsula from Ukraine almost 10 years ago and its forces based there played a big role in the full-scale invasion of Ukraine in February 2022.
The Caesar Kunikov has already been targeted since the war began. It was damaged along with the Novocherkassk in a Ukrainian strike on the occupied port of Berdyansk in March 2022, when a third landing ship, the Saratov, was sunk.