The first units produced for a customer were built in December 1940 and January 1941 for the Atchison, Topeka and Santa Fe Railway and numbered the 100 set.

These were the first diesel-electric locomotives ever produced with dynamic braking, a system developed at the insistence of the railroad and with its assistance.

FTs were generally marketed as semi-permanently coupled A-B sets (a lead unit and a cabless booster connected by a solid drawbar) making a single locomotive of 2,700 hp (2,000 kW).

Some roads, like the initial customer Santa Fe, ordered all their FTs with regular couplers on both ends of each unit for added flexibility.

The FT is very similar to the later F-units in appearance, but there are some differences that render it distinguishable from later EMD freight cab units.

The side panels of the FT were different, but it was fairly common for railroads to alter them to make an earlier unit appear later.

The roof is a more reliable indication; FTs had four exhaust stacks along the centerline (flanked by boxy structures if dynamic brakes were included).

This is not present on the B-units in semi-permanently coupled A-B-A sets, which were called FTSB units (for Short Booster).

As with other early cab units - but unlike "hood" type locomotives - the F (and E) series used the body as a structural element, similar to a truss bridge.

Most of EMD's newer passenger locomotives have a non-structural “cowl” type body built on an underframe derived from freight designs.

First priority for the diesel prime movers' manufacturing capability, as well as the materials used in the fabrication and assembly of the engines, electric generators and traction motors was for military use.

It was also opportune for eastern railroads to stick with coal-fired steam power while petroleum distribution to the east coast was disrupted in early days of the US war effort.

Santa Fe received by far the largest allocation, given its heavy war traffic and the difficulty and expense of providing water for steam locomotives on its long desert stretches.

Other locomotive manufacturers, under extreme competitive pressure from EMD's high-powered and reliable 567 engine in the early postwar era, embarked upon crash development programs that yielded unsatisfactory results.

EMD's advantage resulted in their selling the vast majority of units in the dieselization era and a death spiral for all who tried to compete with them in the early postwar market.