The LNER Class Y1 was a class of 0-4-0 geared steam locomotives built by Sentinel Waggon Works for the London and North Eastern Railway and introduced in 1925.

The superheated vertical water-tube boiler and the engine were similar to those used in Sentinel steam wagons.

There were variations within the class as regards boiler size and fuel capacity and these were denoted by sub-classes Y1/1 to Y1/4.

The engines had poppet valves and reversing was by sliding camshaft.

This article relating to steam locomotives operated in the United Kingdom is a stub.