A Scottish clergyman's 1816 engine now runs silent submarines
In 1816 a Scottish minister, Robert Stirling, patented an engine meant to rival steam. It needed no boiler, burned nothing inside and made almost no noise. For a century it mostly pumped water and blew church organs, but today versions of it let Swedish and Japanese submarines stay submerged far longer.
The trick is a sealed charge of gas that is heated on one side and cooled on the other. As it expands it pushes a piston; a second part called the displacer shuttles it to the cold end, where it contracts and pulls again. Stirling's key addition, which he called an economiser and which is now known as the regenerator, stores heat from the gas during one stroke and hands it back on the next instead of wasting it. Because heat comes from outside, any source will do, from a flame to sunlight, and because the gas never leaves, engineers can pick helium or hydrogen. Spin the shaft by hand and it runs backwards as a heat pump.
An engine built to his design pumped water at an Ayrshire quarry in 1818. His brother James built a larger one for a Dundee foundry in the early 1840s, proving it could deliver industrial power, but parts kept failing under the heat and it was swapped for steam. From about the 1860s small hot-air engines found work where babysitting a steam boiler was impractical, until electric motors displaced them.
Philips revived the idea in the late 1930s, seeking quiet generators for radios where mains power was unreliable. Its 1951 Bungalow set produced about 180 to 200 watts, but only around 150 were built, since transistor radios needed less power. The research later paid off in Stirling-cycle cryocoolers.
Sweden's navy began testing the system at sea aboard Näcken toward the end of the 1980s. The Gotland class, delivered in 1995–1996, burns fuel with liquid oxygen so it needs no outside air. Engineers also pair the engines with solar dishes, and in 2025 researchers ran one on nothing but the chill of radiating heat to the night sky.
Source: Stirling engine
