It looks like the SS Atlantic was a cruise ship back in 1949 so the two sources I gave you may not have information about the passengers since they were not displaced persons (DPs).
Here's some more information about the ship that someone else posted:
The S.S. Atlantic began life as the S.S. Malolo in 1926 , making trips mainly to the Hawaiian islands. In 1937 she was rebuilt and relaunched as the Matsonia, sailing between San Francisco and Honolulu until 1941. She was converted to a troop-ship and was set to head for the Phillipines, but the invasion of Pearl Harbor forced her to turn back. She was used primarily as a troop and weaponry carrier for the duration of the war and then was decomissioned in 1946, and it is estimated that she transported over 176,000 persons, troops, war brides and civilians.
S.S. Matsonia was eventually sold to the Mediterranean Line ( a Panamanian subsidiary of the Home Lines) and was renamed the S.S. Atlantic. She was refitted at Genoa, Italy, departed on May 14, 1949 for her maiden voyage to New York City via Naples and Barcelona. This would have been where the restaurateur came into the picture – signing on as a waiter in the early 50s.
The back of the photo of my father above indicates that his trip was in Mid-May, 1953. This ties in with the recorded information which states that the Atlantic ran voyages after 1952 between Southampton, England and Canada.
In January, 1955, the Atlantic was tranferred to the National Hellenic Line (out of Greece). Am I the only one who thinks these ships really got around? It was renamed S.S. Vasilissa Friederiki for Queen Frederica. Only the English name ever appeared on her bow.
Below is a link to a video I discovered on YouTube under “Queen Frederica”.