Sea Lion, Steam tank locomotive in Groudle Glen, Isle of Man

Sea Lion is a steam tank locomotive on the narrow-gauge Groudle Glen Railway, built in 1896 by W.G. Bagnall & Co. of Stafford. It has a 2-4-0T wheel arrangement and two cylinders, and carries a displacement lubricator on its polished brass dome. Its steam distribution system was patented by E.E. Baguley and survives on only four locomotives.

Built by W.G. Bagnall in 1896, this locomotive was the railway's only engine until Polar Bear arrived in 1905. It marks the start of mechanized service on this historic line.

The locomotive's name is painted in gold letters with blue shading on its side water tank, and it originally carried round "spectacle" windows at the front and rear of the cab. These were replaced early in its career by rectangular windows to improve the driver's view.

The locomotive operates during regular passenger service at Groudle Glen Railway and can be seen in action on the narrow tracks. The sloped terrain and close proximity to the railway require careful footing when viewing or photographing the machine.

Sea Lion kept its original name when it was rebuilt as a battery-electric locomotive in the 1920s, so the steam engine and its electric replacement both carried it. The electric pair proved a financial failure, and the steam locomotive returned to service.