RMS Olympic - the only ocean liner to sink a U-boat. May 12, 1918 she intentionally rammed and sank U-103.
Bingo.
The Olympic was the only of her class (Olympic, Titanic, Britannic), to have any kind of service life. The Britannic struck a mine and sunk in about 1 hour, in spite of having a double hull and re-enforced bulkheads added after the loss of the Titanic.
The Olympic survived a collision with the HMS Hawke, which the admiralty blamed on the Olympic, even though the Olympic had the right of way, and the Hawke cut too close in passing and was sucked into the side of the Olympic by the much larger ships wake. Goes to show you can't fight City Hall, or the Admiralty.
The Olympic had quite the wartime career, delivering troops through contested Mediterranean waters throughout the Gallipoli campaign, and later from Canada and the US to Europe through the remainder of the war. Rammed and sank a German U-Boat that was attempting to line up a torpedo shot on her - unfortunately for the U-Boat, she was unable to flood her tubes in time, and the rather aggressive (for a troopship captain) and quick thinking Cpt. Hayes decided he had better odds of survival by running down the U-Boat. Hayes would be awarded several medals for his career during the war.
Returned to commercial service after the war, she was a successful trans-Atlantic luxury liner for many years to come, unlike her cursed sisters.
Jessop also left service after the war, and remained with White Star for many years, even after it merged with Cunard. Lived to a ripe old age, passing away in 1971, IIRC.