Croatia had no answer to the dynamic duo as England ran out 4-1 winners in their World Cup qualifier on Wednesday.
And Rooney said: "He's got frightening pace. It's probably something different to what we've had for the past four years."
Manchester United ace Rooney believes Walcott is England's missing link in the hunt to end 42 years without victory at a tournament.
He added: "Theo can help us win trophies. He deserves the headlines for scoring three brilliant goals in a tough away game at such a young age.
"He likes to run behind defenders and does something different which keeps them on the back foot.
"I've not seen anyone as quick as him. He scored a goal in training the other week and everyone looked at how quick he was. When he gets going he's just unbelievable."