The BM-21 launch vehicle (Russian: БМ-21 "Град"), a Soviet truck-mounted 122 mm multiple rocket launcher, and a M-21OF rocket were developed in the early 1960s. BM stands for boyevaya mashina, ‘combat vehicle’, and the nickname grad means ‘hail’. The complete system with the BM-21 launch vehicle and the M-21OF rocket has designation as M-21 Field Rocket System. The complete system is more commonly known as a Grad multiple rocket launcher system. In NATO countries, the system (either the complete system or the launch vehicle only) was initially known as M1964. Several other countries have copied it or developed similar systems.

The M-21 Field Rocket System with a BM-21 launch vehicle (122 mm multiple rocket launcher (MRL) system entered service with the Soviet Army in 1963 to replace the aging 140 mm BM-14 system. The launch vehicle consists of a Ural-375D six-by-six truck chassis fitted with a bank of 40 launch tubes arranged in a rectangular shape that can be turned away from the unprotected cab. The vehicle is powered by a water-cooled V-8 180 hp gasoline engine, has a maximum road speed of 75 km/h (47 mph), road range of up to 750 kilometres (470 mi), and can cross fords up to 1.5 m (4 ft 11 in) deep. The original vehicle together with supporting equipment (including the re-supply truck 9T254 with 60 rockets) is referred to by the GRAU index 9K51; the launcher itself has the industrial index of 2B5. In 1976, the BM-21 was mounted on the newer Ural-4320 six-by-six army truck.