Highly efficient multiple expansion steam engines began being used on ships, allowing them to carry less coal than freight. The oscillating engine was first built by Aaron Manby and Joseph Maudslay in the 1820s as a type of direct-acting engine that was designed to achieve further reductions in engine size and weight. Oscillating engines had the piston rods connected directly to the crankshaft, dispensing with the need for connecting rods. In order to achieve this aim, the engine cylinders were not immobile as in most engines, but secured in the middle by trunnions which allowed the cylinders themselves to pivot back and forth as the crankshaft rotated, hence the term "oscillating".