The Britannic, sister ship to the Titanic, sinks in the Aegean Sea on November 21, 1916, killing 30 people. More than 1,000 others were rescued.

In the wake of the Titanic disaster on April 14, 1912, the White Star Line made several modifications in the construction of its already-planned sister ship. First, the name was changed from Gigantic to Britannic (probably because it seemed more humble) and the design of the hull was altered to make it less vulnerable to icebergs. In addition, it was mandated that there be enough lifeboats on board to accommodate all passengers, which had not been the case with the Titanic.

The nearly 50,000-ton luxury vessel, the largest in the world, was launched in 1914, but was requisitioned soon afterward by the British government to serve as a hospital ship during World War I. In this capacity, Captain Charlie Bartlett led the Britannic on five successful voyages bringing wounded British troops back to England from various ports around the world.

On November 21, the Britannic was on its way to pick up more wounded soldiers near the Gulf of Athens, when at 8:12 a.m., a violent explosion rocked the ship. Captain Bartlett ordered the closure of the watertight doors and sent out a distress signal. However, the blast had already managed to flood six whole compartments—even more extensive damage than that which had sunk the Titanic. Still, the Britannic had been prepared for such a disaster and would have stayed afloat except for two critical matters.

First, Captain Bartlett decided to try to run the Britannic aground on the nearby island of Kea. This might have been successful, but, earlier, the ship’s nursing staff had opened the portholes to air out the sick wards. Water poured in through the portholes as the Britannic headed toward Kea. Second, the disaster was compounded when some of the crew attempted to launch lifeboats without orders. Since the ship was still moving as fast as it could, the boats were sucked into the propellers, killing those on board.

Less than 30 minutes later, Bartlett realized that the ship was going to sink and ordered it abandoned. The lifeboats were launched and even though the Britannic sank at 9:07, less than an hour after the explosion, nearly 1,100 people managed to make it off the ship. In fact, most of the 30 people who died were in the prematurely launched lifeboats. In 1976, famed ocean explorer Jacques Cousteau found the Britannic lying on its side 400 feet below the surface of the Aegean. The cause of the explosion remains unknown, but many believe that the Britannic hit a mine.