In 1834, the engine was selected for further (unsuccessful) modifications to test a newly developed rotary steam engine designed by Admiral The 10th Earl of Dundonald. At a cost of nearly £80, "Rocket"s cylinders and driving rods were removed and two of the engines were installed directly on its driving axle with a feedwater pump in between. On 22 October, of that year, an operational trial was held with disappointing results; one witness observing, that "the engine could not be made to draw a train of empty carriages". Due to inherent design flaws and engineering difficulties associated with their design, Lord Dundonald's engines were simply too feeble for the task.