I will go out on a limb and state my considered opinion that both Rock Around the Clock and That's All Right are western swing. Their main significance is that

I will go out on a limb and state my considered opinion that both Rock Around the Clock and That's All Right are western swing. Their main significance is that they perfected the genre and made improvements impossible. So Elvis had to invent rock 'n' roll with his next single, Good Rockin' Tonight.