Victor released a pop version of the song by "The Turtles" with backing by the Winterhalter ork (Victor 6356) in December 1955. Billboard wrote that Presley's version had "cut a swath in the country field." Paired with "I Forgot to Remember to Forget", the record was in the Top 10 in Billboard's C&W listings.
RCA Victor rereleased this recording in December 1955 (#47-6357) after acquiring it as part of a contract with Presley. This issue of the song peaked at # 11 on the national Billboard Country Chart.
Although "Mystery Train" is now considered to be an "enduring classic", the flip side of this record "I Forgot to Remember to Forget" reached the Billboard National Country music chart #1 position by February 1956, remained there for 5 weeks, and stayed on the charts for 39 weeks. The May 12, 1956 issue of Billboard listed "I Forgot to Remember to Forget" at the #1 "Country & Western" "Top Juke Box Hit Records" for the period January-April 1956 with no mention of "Mystery Train". It was the first recording to make Elvis Presley a nationally known country music star.
One commentator noted "One of the mysteries about 'Mystery Train' was where the title came from; it was mentioned nowhere in the song". The song uses lyrics similar to those found in the traditional American folk music group Carter Family's "Worried Man Blues", itself based on an old Celtic ballad, and their biggest selling record of 1930:
The train arrived sixteen coaches long The train arrived sixteen coaches long The girl I love is on that train and gone
Black, who had success with the Bill Black Combo, once said to a visitor to his house in Memphis, as he pointed to a framed 78rpm Sun Record of "Mystery Train" on the wall, "Now there was a record."
Presley's version of the song was also ranked the third most acclaimed song of 1955, by Acclaimed Music.
~Source wikipedia