A major flaw with the design of cab units, such as the EMD F series or ALCo FA series, was the poor visibility to the rear. Another was that there wasn't a place for the brakeman to stand on either end. ALCo responded with the RS series starting in 1941, but EMD didn't make a roadswitcher until 1948. That was when EMD built the prototype for the BL2, the BL1.
The BLs were based on the F3, a cab unit. EMD added platforms on both ends for the brakeman and also put notches into the body so the crew could see the brakeman out on the platform. EMD also tried to make it appealing to passengers in case it was used for passenger service.
The BLs kept the same electronics and engine as the F3, and even kept the original trusses which function as a frame. The F3 used most of the body as the frame, whereas the BL only used the trusses. This made the frame weaker, which made it impossible to MU with more than one other engine. This made it less appealing to the railroads.
Everything in the original F3 was also squeezed to about half the width, making maintenance harder. It was also impossible to take off the sides like it was in the RS-3, because the frame was there; and without a frame, it could fall apart.
Production of the BL2 ended in 5/1949, and a few months later, the GP-7 was available. The GP-7 took advantage of the lessons learned from the BL-2 and sold well until it was superceded by the GP-9, which sold over 4000 units.
Number built: 58
Powerplant: 567B
Horsepower: 1500
Tractive Effort: ~60,000#
Top speed (62:15) 66 mph