on a train included only F-units, the train would then be called a wagon train. Those two usages are still popular with the railfan community. Models Model development The FT, introduced in 1939 with the new 567 engine and Blomberg B trucks, was a successful design, and remained in production during WWII. The F3 (1946) had a different roof arrangement that included the replacement of the FT's boxy dynamic brake structure with two under-roof grids, two exhaust stacks instead of four, and four cooling fans grouped together instead of separated pairs of cooling fans. The F3 was also longer than the FT to allow a standard draft gear to be installed at the rear of the unit. The 567B engine was uprated to . Some F3s were nicknamed "chickenwire" for the type of engine room air-intake structure along the sides. The F7 (1949) and F9 (1954) were evolutionary: the F7 had improved traction motors, the F9 a 567C engine. A louver arrangement over the vents changed their appearance from the F3. There were also versions, the FP7 and FP9, the extra length being used to house a tank for extra water capacity. Only one F model did not have Blomberg B trucks: the FL9 electro-diesel locomotive had a lightweight Flexicoil B in front and a standard passenger A-1-A at the rear. Model descriptions are as built, but EMC/EMD locomotives are often rebuilt to newer standards. Engine and powertrain The F series used a 16-cylinder version of the 567 series diesel engine, introduced in 1939. The 567 was designed specifically for railroad locomotives, a mechanically aspirated 2 stroke 45 degree V type with displacement per cylinder, for a total of . An ongoing engine improvement program saw the FT’s original up-rated to in the FL9 by the end of F unit production. A DC generator powered four traction motors, two on each truck. The Blomberg B truck first used in the FT became the EMD production standard, being used until 1995. EMC/EMD built all of its major components after 1939 Passenger service While the F-unit series was originally conceived for freight service, many were used to haul passenger trains. The original EMC FT demonstrator was equipped with a steam generator in the B units for train heating. Several railroads took advantage of the large space in the rear of their B units to add steam generators. The first FTs built strictly