The E9 is a 2,400-horsepower (1,790 kW), A1A-A1A passenger train-hauling diesel locomotive built by General Motors' Electro-Motive Division of La Grange, Illinois, between April 1954 and January 1964.

Designed specifically for railroad locomotives, this Roots-blown, mechanically aspirated 2-stroke 45-degree V-type, with an 8+1⁄2 by 10 in (216 by 254 mm), bore by stroke, giving 567 cubic inches (9.29 L) displacement per cylinder, remained in production until 1966.

Many of America's finest trains — such as Union Pacific Railroad's "City" fleet, Burlington's "Zephyr" fleet and Southern Pacific Railroad's Coast Daylight and Sunset Limited — had E9s pulling them.

As America's passenger train network shrank due to unprofitability, Union Pacific, Rock Island and Illinois Central began using E9s on freight trains while Burlington Northern began upgrading their fleets of E9s with Head-end power and EMD 645 power assemblies for commuter operations in the Chicago metropolitan area into the early 1990s.

Amtrak used the E9s until 1979 and converted some E9B units to steam generator and head end power cars.