In 1963, CKD began supplying a diesel locomotive for heavy shunting and local freight trains, of which around 8,200 were ultimately built for several Eastern Bloc countries. They were designated ЧМЭ3 in the Soviet Union, which led to the nickname “Cmelak” (bumblebee) in Czechoslovakia. The CSD tested one locomotive in 1963 and decided to order more locomotives with adjustments to their own requirements.
The basic design of these locomotives corresponded to American road switchers. This means they had a supporting frame, narrower, taller hoods and a cab that was shifted towards one end. This layout was created at the request of the Soviet Union, since they had already received locomotives from ALCO in World War II. Like the American locomotives, they had a medium-speed diesel engine with a displacement of 163 liters and a turbocharger. In contrast to these, however, the cab was relatively well insulated and soundproofed.
Due to a lack of production capacity at CKD, the first production locomotives for the CSD were not made until 1967 at SMZ in Dubnica in what is now Slovakia. Around 120 examples were built there until 1969, when a new type of bogie suspension was developed. The modified variant was built a total of 324 times by 1972. The older ones were named T 669.0 and the newer ones T 669.1 to distinguish them. In 1977 and 1979, CSD received a T 669.0 each from CKD. A total of 25 of the two variants were built for the 1,520 mm broad gauge, which had to shunt freight trains from the Soviet Union weighing up to 4,000 tonnes in the east of the country.
The T 669.2001 was built with an engine that was set at 1,500 hp but later reset. When the numbering system was changed in 1988, the T 669.0 and T 669.1 were renumbered as the classes 770 and 771. In the Czech Republic, the CD retired the locomotives by 2005 because shunting locomotives of this size were no longer needed. The situation was similar in Slovakia, but the broad-gauge machines were still needed in the east, and they were also occasionally used after 2010. Others were sold to private customers and some were fitted with more modern engines.