>Can you guess what they were in their previous lives?
The first MERCY (AH 4) was built in 1907 as SARATOGA by William Cramp & Sons, Philadelphia, PA. An Army troop transport in the first nine months of World War I, she was renamed MERCY and converted to a hospital ship at New York Navy Yard, Brooklyn, N.Y.
>sauce:
https://www.msc.usff.navy.mil/Ships/Mercy/History/