The Austrian dreadnought SMS Viribus Unitis was gifted to Yugoslavia in 1918, and then blown up by an Italian manned torpedo less than a day later.
Not too long ago I discovered that manned torpedoes exist. They are essentially miniature submarines, piloted by one or two people in wetsuits. The torpedoes were perfect for stealth missions: they could sneak up on an enemy ship without being detected. The divers would attach a limpet mine to the side of the ship and swim away. It was not a suicide mission, although many divers died anyway. The human torpedo had is heyday in World War II, but the Italian navy had some success with early prototypes in World War I. Their greatest success: the sinking of the SMS Viribus Unitis.
In 1918, the Austro-Hungarian Empire was in big trouble. Their armies had been so poorly commanded that the loss of the war and the collapse of the empire was inevitable. The Austrian navy was concerned that their inevitable defeat would mean the surrender of its ships. And so they decided to gift them to the newly-formed country Yugoslavia (at the time known as the State of Slovenes, Croats and Serbs; it was formerly a part of the collapsing Austro-Hungarian Empire). To their thinking, it was better to have the ships in the hands of a relatively neutral party than the enemy they had been fighting for four years.
The dreadnought battleship SMS Viribus Unitis was the pride of the Austro-Hungarian navy. When Archduke Ferdinand was assassinated (triggering World War I), his body travelled back to Trieste on this ship. So it must have been difficult to give it away. But they did, and on the evening of October 31st, 1918, it was officially renamed Jugoslavija and the newly appointed naval commander-in-chief of Yugoslavia, Janko Vuković, took over the ship. It would be one of the shortest naval tenures in history.
The Italian navy had not heard about the transfer. As far as they knew, the dreadnought was still Austro-Hungarian and therefore a valid target. And they happened to have a prototype human torpedo ready to go. That same night, two Italians pulled up alongside the ship on a torpedo. They attached a limpet mine to its side; a second limpet mine was dropped directly underneath the hull. And here’s the real kicker: they were both caught.
The two Italians were hauled up for questioning. They admitted that they had planted bombs, but refused to give up the exact location. The mines had been planted at 4:40am; they were set to go off at 6:30am. Vuković sprang into action and ordered an evacuation.
6:30am came and went with no explosion. Vuković was wondering whether the Italians were bluffing. The Italians were wondering if they had messed up the timer. The bomb went off at 6:44am instead; most of the Yugoslav crew were still on board. Scuppered, the dreadnought sank in a few minutes, taking hundreds of men and the commander-in-chief with it. The Italians both survived. Two days later the Austro-Hungarian Empire’s armistice was accepted and the war, for them, ended.