The BM-21 launch vehicle (Russian: БМ-21 "Град"), (Grad) 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 Systems 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.
The crew of 3 men can emplace the system and have it ready to fire in three minutes. The crew can fire the rockets from the cab or from a trigger at the end of a 64-metre (210 ft) cable. All 40 rockets can be away in as little as 20 seconds, but can also be fired individually or in small groups in several-second intervals. A PG-1M panoramic telescope with K-1 collimator can be used for sighting. The BM-21 can be packed up and ready to move in two minutes, which can be necessary when engaged by counter-battery fire. Reloading is done manually and takes about 10 minutes.
Each 2.87-metre (9 ft 5 in) rocket is slowly spun by rifling in its tube as it exits, which along with its primary fin stabilization keeps it on course. Rockets armed with high explosive/fragmentation, incendiary, or chemical warheads can be fired 20 kilometres (12 mi). Newer high explosive and cargo (used to deliver anti-personnel or antitank mines) rockets have a range of 30 kilometres (19 mi) and more. Warheads weigh around 20 kilograms (44 lb), depending on the type.
The number of rockets each vehicle is able to quickly bring to bear on an enemy target make it effective, especially at shorter ranges. One battalion of eighteen launchers is able to deliver 720 rockets in a single volley. The system has lower precision than a classical artillery and cannot be used in situations that call for pinpoint precision. It relies on a large number of shells to dissipate over an area for a certain hit rate on specific targets. Nonetheless, because of the short warning time for the impact of the whole volley the BM-21 is considered a fearsome weapon until today.
BM-21-1 launch vehicle during a military parade in Yekaterinburg, 9 May 2009.
9P138 launch vehicle of the Grad-1 multiple rocket launcher system.
- BM-21: Original version known as the BM-21 launch vehicle. The launcher unit was mounted on a modified Ural-375D truck chassis.
- BM-21-1: Launch vehicles are mounted on a family of Ural-4320 truck chassis.
- 2B17 or also BM-21-1: This upgrade was presented for the first time in 2003 and was developed by Motovilikha Plants from Perm. The system is fitted with a satellite navigation system NAP SNS, automated fire control system ASUNO, APP laying system and can fire a new generation of rockets with a range of 40 km (25 mi). The truck is the Ural-43201.
- 9P138 "Grad-1": lighter 36-round version, mounted on a six-by-six ZIL-131 chassis. The vehicle with supporting equipment (rockets, transporter 9T450 and re-supply truck 9F380) is referred to as complex 9K55. The 9P138 can only use "short-range" rockets with a range of 15 km (9.3 mi). It used to be known in the West as BM-21b or M1976.