The EMD Model 40 was a two-axle diesel-electric switcher locomotive built by Electro-Motive Corporation (EMC), and its corporate successor, General Motors' Electro-Motive Division (EMD) between August 1940 and April 1943.

Nicknamed "critters", eleven examples of this locomotive were built.

Powered by twin General Motors Detroit Diesel 6-71 diesel engines, which produce a combined 300 horsepower (224 kW), its drivetrain is unusual because the two diesel engines are used to drive the electric DC generator from both sides, one with clockwise rotation and the other with counter-clockwise rotation.

Original buyers for the Model 40 included the Electro-Motive Corporation/Electro-Motive Diesel Plant, 1 unit (used as the #2 plant switcher), Defense Plant Corporation, 4 units, the United States Army, 3 units, the United States Navy, 2 units, and the General Motors Cleveland Diesel Division, 1 unit.

In total EMC/EMD manufactured eleven Model 40s during the period April 1940 - April 1943.