The serve is her signature and a statement. It is technique married to timing and is a first cousin to Joe Frazier's left hook. It comes from a player not particularly tall, 1.75m, but is simple in its toss and classic in its execution.
But if it is rapid, it is no longer reliable. And if Serena Williams wants to win her 24th Grand Slam singles title at Wimbledon then she has to find this serve.