The Shay was the most numerous and best-known type of geared steam locomotive. Its geared drive made it especially effective on steep grades, sharp curves, and lightly built industrial railways.
Developed by Ephraim Shay and manufactured by Lima Locomotive Works, the design used an offset boiler and a multi-cylinder engine driving a longitudinal shaft. Bevel gears then powered the axles, allowing the locomotive to apply power to all its driven wheels rather than relying on conventional side rods.
Shays were widely used in logging, mining, quarrying, and plantation work. Their low-speed pulling power mattered more in those settings than high speed. Climax and Heisler locomotives were important competing designs, while Willamette built a limited number of improved Shay-like locomotives after key patents expired.
A common mix-up is treating all geared locomotives as Shays. “Geared” describes the drivetrain principle; Shay identifies one particular and especially successful design. Shay locomotives were also exported to roughly 30 countries.