@ossobuco,
PrettyhHard to say what the first Rock & Roll song was as the genre evolved over time. Some attribute it to Fats Dominos song - some give it to Ike Tuner's in 1951 for
Rocket 88'' with the Kings of Rhythm (Chess records released it under "Jackie Brenston and His Delta Cats", the drummer's name).
What RATC had the distinction of after being featured in Blackboard Jungle in '55, 1 yr after it was released as a minor hit) that it became the first number one hit for Rock & Roll, thus moving Rock to the mainstream forefront to stay for about 55 years. Prior to that none of the other songs had such broad acceptance and/or had become national number one hits.