EMD's diesel program was well underway by the late 1940s thanks to the success of the company's
F- and
E-units. While the F-units in production were great for moving trains over the railroad, their full-width carbody made it difficult for locomotive crews to see to the rear of the locomotive while switching. This was considered an acceptable sacrifice for a mainline locomotive, which was expected to do little switch work, since the full-width carbody type was considered much more handsome and stylish. By 1948, competitors
Alco,
Baldwin, and
Fairbanks-Morse had introduced
road switcher locomotives, which used the narrow hood and full walkway of a
switcher locomotive with a longer frame and the high-speed
trucks of a road locomotive. These locomotives were successful at displacing steam from secondary services such as local and branch-line work. EMD developed the BL1, basing it on the
F3 and using the same bridge-truss
carbody construction as the F-unit (as opposed to the weight-bearing frame of a true
road switcher locomotive like the
Alco RS-1) with the body cut away behind the cab to provide visibility to the rear. The first BL1 was EMD Demonstrator #499, built in September 1947. The BL1 Demonstrator was EMD Project 89499, thus the 499 Demonstrator number. The BL in the model name stood for "Branch Line", indicating that EMD felt the locomotive was best suited for light traffic and frequent switching chores. Limiting the locomotive's success were several mechanical and ergonomic drawbacks. The BL2 was expensive and time-consuming to build because of its unique carbody design. Rather than being built in small segments which could be moved to another area for final assembly, the BL2 had to be built entirely in once place. The mechanical components in the engine compartment were difficult to access and maintain, reducing its appeal among railroad shop crews. The locomotive's carbody lacked the full-length walkways of a true switch engine (a mistake not repeated on the subsequent "GP" series of diesels or other road switchers), making it difficult for the brakeman or switchman to move from one point on the locomotive to another during switching operations. Finally, although the industrial designers at EMD tried to build a carbody that evoked high-class passenger trains while retaining the utilitarianism of railroad work, the design never became popular. EMD applied the lessons learned from the BL2's lack of success in developing the
GP7. ==Original owners==