From 1968 onwards, the SJ had the T44 built for light freight traffic, which has four axles and a central cab. The engine is an EMD 645 series two-stroke with twelve cylinders. With a production run of 123 in 21 years, it is the most numerous diesel locomotive that the SJ has ever purchased. In addition to freight traffic, they were also used in shunting and, if necessary, in front of passenger trains. In the new millennium, a large number came to private operators, most of them to Green Cargo. The decision was made there in 2007 to equip 100 locomotives with new four-stroke engines and to modernize them in other areas. By 2012, 62 units had been rebuilt in this form and were now given the designation Td.

The first diesel locomotives were already being built in the Soviet Union in the 1920s, but these were only built as prototypes or in very small numbers. When the production of the Э^эл was stopped after 46 examples in 1941, no more diesel locomotives were built in the country. ALCO and Baldwin locomotives were soon ordered in the USA, with ALCO's RSD-1 prevailing. Of the 70 pieces sent to the Soviet Union, 68 actually arrived and some continued to serve until the 1980s. After the end of the war, the decision was made to build own locomotives based on the RSD-1 as soon as the locomotive factory in Charkiv was rebuilt. The production of the engine using new production methods presented a challenge, but finally the first locomotive of the series initially designated ТЭ1-20 (TE1-20) was delivered in 1947. The designation was made up of “diesel-electric number 1” and the axle load of around 20 tonnes. Later the 20 was omitted from the designation.

Generally speaking, the ТЭ1 corresponded to the RSD-1, which was in service in the Soviet Union as Д^a. The engine was essentially the same as the ALCO 539T and, like this, delivered 1,000 hp. The other assemblies were mostly adopted with minimal changes, but first converted to the metric system and thus deviated by a few millimeters from the American parts. Not only in general construction, but also in optical details, the Soviet locomotive corresponded almost completely to its prototype. This meant a wide driver's cab with a barrel-shaped roof at one end of the locomotive, followed by a narrower, long and short body respectively. The existing American-made locomotives were gradually retrofitted with assemblies based on the metric system as part of maintenance work and were thus adapted to the ТЭ1.

The diesel locomotives were often used in regions where the water supply for steam locomotives was difficult. Some were also used in the greater Moscow area or for shunting, and by 1950 almost 300 examples had been built. The ТЭ5 was built in small numbers as a variant for extremely cold climates. The driver's cab was extended with a longer housing, which protected the engine, including the turbocharger, and the battery from the cold. To test the use of coal in diesel engines, 16 examples were converted to gas generator locomotives ТЭ1^Г and dismantled again after the end of the trials. The shunting locomotive ТЭМ1 followed only eight years after the end of production of the ТЭ1, whose developments with a similar appearance are still being built today. The direct successor to the ТЭ1 was the ТЭ2, which used almost the same technology but consisted of two sections.

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.