Patentee

The Planet design of 1830, though revolutionary, was limited by its short wheelbase: as boilers grew larger to deliver more steam, the engine became unstable at speed. Robert Stephenson's solution, patented in 1833 and giving the class its name, was to add a single pair of carrying wheels behind the firebox, producing a 2-2-2 layout with the firebox suspended between the driving and trailing axles. The longer wheelbase improved stability, allowed a larger boiler and firebox, and gave more room for water and coal.

The Patentee proved enormously influential: it was supplied to the London & Birmingham, the Grand Junction, the early GWR (as the broad-gauge Star class), and to railways in Belgium, the Netherlands, Germany, Russia, and Austria. Over 70 were built between 1834 and 1840.

The Patentees were the standard British express engine of the 1830s, working passenger trains on every major main line as it opened. They were progressively replaced by larger 2-2-2s and Bury bar-frame engines from the 1840s onwards, but many lasted until the 1850s, and several of the Continental examples remained in service even longer. None of the originals were preserved, but the layout was the direct ancestor of every 19th-century British single-driver express engine.

2-2-2 layout with a single pair of large driving wheels (typically 5 ft 6 in to 6 ft 0 in), inside cylinders at the smokebox end, and a long Stephenson sandwich frame extending the full length of the engine. The trailing carrying axle distinguishes the class from the earlier Planet.

• Patentee (1834, not preserved)
• Replica of broad-gauge Patentee variant (North Star) at STEAM Swindon