In 1829 Rocket it took part in, and won the Rainhill trials to find the best locomotive of the day for the Liverpool and Manchester Railway. This was the World's first inter-city line and used steam locos exclusively.

Not only that, but 'Rocket' established some design features that would stay the distance for steam loco design. In particular, it had a fire tube boiler with a separate, water jacketed firebox. It had what Robert Stephenson described as 'working gear'. This was a valve operating mechanism that made it easier to change from forward to reverse, with eccentrics on the driving axle and reverse and forwards links changed by a foot pedal on the footplate floor.

All this was prototype work. The original 'Rocket' looks different and shows how the design developed. Look at the original loco that survives in London's Science Museum and you'll see that it has a proper smokebox and the cylinders are mounted horizontally. These were developments from operating experience and were applied to 'Rocket's sister locos like 'Northumbrian'.

Development was rapid at that time and by 1830, 'Planet' appeared from Stephenson's Newcastle upon Tyne works, looking much more like the steam loco that we all know. Only a replica exists at Manchester Museum of Science and Industry. You can see it on this website.