"Roll out" is a common command among Transformers (primarily the Autobots), essentially meaning to move out, deploy or otherwise embark on a mission. Its literal meaning, to start rolling in one's ground-based, wheel-equipped vehicle mode, appears to have become diluted over time, to the point that Transformers who don't even have vehicular alternate forms (and have to run to where they're going) still give/receive the order.
Generation One cartoon
The phrase in its most iconic form was uttered by Optimus Prime; it typically signified the start of a mission, as the group transformed and deployed to counter the Decepticons' latest scheme.
It was such a famous command that, in the months following Optimus Prime's death, Pipes rallied his troops to defend Autobot Headquarters thus: "As Optimus Prime used to say, transform and roll out!"
Marvel Comics continuity
The phrase here was less associated with Optimus Prime, though he did use it to start off several missions in the months after he was returned from Shockwave's captivity. In fact, the first known utterance of the phrase was by Wheeljack, as he and Jazz left the Ark on a mission.
Later it would be used to command all sorts of Transformers to do all sorts of things, such as running to one's destination, or leaping out of a starship into space.
Though it would seem logical, nobody has ever told Retrax to "roll out". Not too many other Beast Warriors are much equipped to do so.
Transformers (2007 movie)
Optimus Prime used a version of the catchphrase twice in the movie, once at the observatory, shortened to "Autobots, roll out!", and earlier when transforming to escape from Sector Seven as just "Roll out!". 'Transforming' in either case must have seemed too obvious to mention.
Repair crew captain Optimus Prime, once settled/stranded on Earth, typically used the command "Transform and roll out!" to have his squad deploy on a mission. adoring young fans among the population of Detroit requested that he say the phrase for them. Ultra Magnus later told Jazz to "Transform and roll out" when he decided that the two of them should deal with a runaway train.It became such a catchphrase for him that his
The Decepticons have their own version of the command: "Transform and rise up!" Megatron, Blitzwing, Lugnut and Starscream) have flying vehicle modes, hence the reason for the variation of the Command.It is also interesting to note that most of the Animated Decepticons (