The TU7 (ТУ7) was developed in 1971–1972 at the Kambarka Engineering Works to replace the aging locomotive classes TU4 (ТУ4) and TU2 (ТУ2). There were 3,361 locomotives constructed, of which several hundred were exported to the countries of the socialist community and affiliated countries. The TU7 - TU7A (ТУ7 - ТУ7А) was designed to be used on any gauge from 750 mm (2 ft 5+1⁄2 in) to 1,435 mm (4 ft 8+1⁄2 in). In 1986 the locomotive design was updated and designated type TU7A (ТУ7А).
The D4H 1,000 mm (3 ft 3+3⁄8 in) and 9 locomotives D4Hr for standard gauge 1,435 mm (4 ft 8+1⁄2 in), also known as the TU7 - TU7A (ТУ7 - ТУ7А) diesel locomotive,[1] is a series of diesel locomotives currently used on the Vietnamese railway network. With 77 1,000 mm (3 ft 3+3⁄8 in) D4H locomotives in service throughout the country as of 2005, it is the most common locomotive class used in Vietnam.[1] The series was originally procured from the Soviet Union after the Vietnam War.