ℹ️ ➖➖➖ 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 ageing 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 three-member crew 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-meter (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 a 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-meter (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 that each vehicle is able to quickly bring to bear on an enemy target makes 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 typical artillery and cannot be used in situations that call for pinpoint accuracy. It relies on a large number of shells dissipating 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 still considered an effective weapon.

🛠 Manufacturer Splav State Research and Production Enterprise
▪️✅ Produced 1963–present
▪️⬇️ Mass 13.71 tonnes (30,225 lb)
▪️📏 Length 7.35 m (24 ft 1 in)
▪️📏 Barrel length 3.0 m (9 ft 10 in)
▪️↔️ Width 2.40 m (7 ft 10 in)
▪️↕️ Height 3.09 m (10 ft 2 in)
▪️👤 Crew 3
▪️↗️ Barrels 40
▪️⏫ Rate of fire 2 rounds/s
▪️⏭ Muzzle velocity 690 m/s (2,264 ft/s)
▪️🔝 Maximum firing range 20 km (12 mi) (new rockets 30–45 km)
▪️⏺ Sights PG-1M panoramic telescope
▪️⚙️ Engine V-8 gasoline ZiL-375 180 hp (130 kW)
▪️🔂 Suspension 6×6 wheeled
▪️🛢 Operational range 405 km (251 mi)
▪️⏩ Maximum speed 75 km/h (47 mph)

Ref: Wikipedia.