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Katyusha multiple rocket launchers (Russian: Катюша) are a type of rocket artillery first built and fielded by the Soviet Union in World War II. Compared to other artillery, these multiple rocket launchers deliver a devastating amount of explosives to an area target quickly, but with lower accuracy and requiring a longer time to reload. They are fragile compared to artillery guns, but inexpensive and easy to produce. Katyushas of World War II, the first self-propelled artillery mass-produced by the Soviet Union, were usually mounted on trucks. This mobility gave Katyushas (and other self-propelled artillery) another advantage: being able to deliver a large blow all at once, and then move before being located and attacked with counter-battery fire. Katyusha weapons of World War II included the BM-13 launcher, light BM-8, and heavy BM-31. Today, the nickname is also applied to newer truck-mounted Soviet multiple rocket launchers—notably the common BM-21—and derivatives. Initially, the secrecy kept their military designation from being known by the soldiers who operated them. They were called by code names such as Kostikov Guns (after the head of the RNII), and finally classed as Guards Mortars. The name BM-13 was only allowed into secret documents in 1942, and remained classified until after the war. Because they were marked with the letter K, for Voronezh Komintern Factory, Red Army troops adopted a nickname from Mikhail Isakovsky’s popular wartime song, Katyusha, about a girl longing for her absent beloved, who is away performing military service. Katyusha is the Russian equivalent of Katie, an endearing diminutive form of the name Katherine: Yekaterina →Katya →Katyusha. German troops coined the sobriquet Stalin’s organ (German: Stalinorgel), after Soviet leader Joseph Stalin for its visual resemblance to a church musical organ and alluding to the sound of the weapon’s rockets. They are known by the same name in Sweden. The heavy BM-31 launcher was also referred to as Andryusha (Андрюша, “Andrew”, endearing diminutive). Katyusha rocket launchers were mounted on many platforms during World War II, including on trucks, artillery tractors, tanks, and armoured trains, as well as on naval and riverine vessels as assault support weapons. The design was relatively simple, consisting of racks of parallel rails on which rockets were mounted, with a folding frame to raise the rails to launch position. Each truck had between 14 and 48 launchers. The 132-mm diameter M-13 rocket of the BM-13 system was 180 centimetres (70.9 in) long, 13.2 centimetres (5.2 in) in diameter and weighed 42 kilograms (92 lb). Initially, the caliber was 130 mm, but the caliber was changed (first the designation, and then the actual size), to avoid confusing them with regular artillery shells3. It was propelled by a solid nitrocellulose-based propellant of tubular shape, arranged in a steel-case rocket engine with a single central nozzle at the bottom end. The rocket was stabilised by cruciform fins of pressed sheet steel. The warhead, either fragmentation, high-explosive or shaped-charge, weighed around 22 kg (48 lb). The range of the rockets was about 5.4 kilometres (3.4 mi). Later, 82-mm diameter M-8 and 310-mm diameter M-31 rockets were also developed. The weapon is less accurate than conventional artillery guns, but is extremely effective in saturation bombardment, and was particularly feared by German soldiers. A battery of four BM-13 launchers could fire a salvo in 7–10 seconds that delivered 4.35 tons of high explosives over a four-hectare (10 acres) impact zone.2 With an efficient crew, the launchers could redeploy to a new location immediately after firing, denying the enemy the opportunity for counterbattery fire. Katyusha batteries were often massed in very large numbers to create a shock effect on enemy forces. The weapon’s disadvantage was the long time it took to reload a launcher, in contrast to conventional guns which could sustain a continuous low rate of fire. The sound of the rocket launching also was unique in that the constant “woosh” sound that came from the firing of the rockets could be used for psychological warfare. The rocket’s devastating destruction also helped to lower the morale of the German army.