The M62 is a Soviet-built diesel locomotive for heavy freight trains, exported to many Eastern Bloc countries as well as to Cuba, North Korea and Mongolia.

[1] According to the Comecon directives production of heavy diesel locomotives among Eastern Bloc countries was left exclusively to Romania and the Soviet Union.

In Poland those machines received ST44 designation[4] During first-revision repairs all locomotives had front lights changed from small ones into standard, Polish large types.

Deliveries continued until 1988, with 1,191 locomotives delivered in total (1,114 for PKP standard-gauge network, 68 broad-gauge units for LHS and 9 for the industry).

One of the locomotives (ST44-1500 – producer's designation M63) had newer bogies and traction engines, allowing it to reach a higher top speed.

Many machines withdrawn from PKP found their place among industrial and private railways, where they only bore the producer's M62 designation.

[3] The locomotives that are still in use in large numbers, are owned and operated by private railroad companies, as well as the LHS broad gauge line.

[6] Since 2007 Newag offers extensive modernisations of the M62 locomotives that involve the replacement of the prime mover and generator, fitting new drivers' cabs and new body.

[8] In 2017 Polish train operator Rail Polska [pl], in co-operation with VIS Systems, converted one ST44 to 3 kV DC electric.

The new locomotive, designated 207E, uses the original's bogies and underframe; it develops 2.4 MW (3,200 hp) power and has maximum speed of 100 km/h (62 mph).

[12] Because of its low maintenance requirements the M62 locomotive is quite popular with the Korean State Railway of the North Korea, where they serve not only on non-electrified lines but on electrified ones as well.

[13] Locomotive Naeyŏn 602 has a special red tablet mounted on it that states that this machine was personally inspected by Kim Il-sung.

A program to replace the original, very outdated two-stroke Kolomna 14D40 power plants with a modern, more efficient engine was started in 1997, with the first locomotive, M62 301 debuting in early 2001.

1972 also the Raab-Oedenburg-Ebenfurther Eisenbahn (Győr-Sopron-Ebenfurti Vasút, GySEV), an Austro-Hungarian joint venture, received six standard-gauge locomotives named M62.9.

[5] In Hungarian service, the M62 proved inferior to the Swedish-American NOHAB M61, which, while 10 tons lighter and slightly less powerful, could haul 25% more weight with 50-60% of the Soviet engine's fuel consumption.

The M62 was unable to run from Budapest to Nyíregyháza and back without refueling, which led to congestion and timetable problems when the NOHAB was replaced by the M62 on that route.

In the 1950s domestically built Soviet diesel locomotives, having the wider 1,520 mm (4 ft 11+27⁄32 in) track base and taller tunnel clearances, used vertical opposed-piston engines.

The Soviet opposed-piston engines, like their US counterparts, were simply too tall to fit in locomotives designed for the 1,435 mm (4 ft 8+1⁄2 in) standard-gauge railways with the tighter tunnel allowances of Eastern Bloc satellite countries.

After the fall of the Soviet Bloc, 31 units of MÁV's M62 fleet were rebuilt with Caterpillar engines in the 1990s, but lack of funds stopped further upgrades.

This proved to be a costly solution, in contrast to the M61 NOHAB, which could produce 750 kg of steam per hour using an internal water tank and engine waste heat, with minimal effects on fuel consumption.