The less famous larger sister ship of Titanic. She too found her end at the bottom of the sea, but was in warmer, Greek waters during World War I, when she struck a mine. Despite her improvements over her demised sister, she sank in only 55 minutes, serving as a hospital ship in war time. She was not too far of the coast, in the Aegan Sea, and like the Cunard rival Lusitania, the captain as stupid enough to try to beach her instead of launching the lifeboats initially. Britannic must have suffered a large explosion, which unabled her watertight doors to function, and open portholes let more water in, and she rolled on her side when her bridge was under water, her captain surviving,
Because the lifeboats were launched without captain's orders whilst he still kept the ship moving, which didn't work as she was sinking, some boats were caught in the propellors, killing at least 30 occupants. All the others onboard made it off safely.
The Britannic had originally been planned to be even more luxurious than Titanic but had to be fitted out for transport of the wounded. However she must have secretly carried illegal munitions, just like the Lusitania which sank one year prior at the Irish Coast after a German submarine, the U-20 had torpedoed her and caused a violent explosion which made her sink very rapidly. That too could have been caused by said hidden ammunition.