In March 1928, as a consequence of the research carried out by V. Artomiev and N. Tikomirov, it was produced in the Gas Dynamics Laboratory of Leningrad a rocket projectile of caliber 82 millimeters, with more than satisfying stability on its trajectory, and with a range of five to six kilometers. These positive results led to intensify the efforts of the several research groups which in that period carried out experiments about rocket propulsion, and in 1934 it was decided to unify the investigations of these groups under the direction of Engineer Petropavlovsky, who would be succeeded by Engineer Kostikov after his death. Finally, in 1938, by taking guidance from former experiences, frameworks initially defined as "launchers for rocket-propelled mines" would be built, from which the BM (initial letters of Boievaia Mashina, meaning Combat Machine) would be finally derived. The acronym was followed by a number which indicated the model of the weapon. This way we have the BM-8, the BM-13 and later the BM-31. Substantially, the BM, which would be familiarly known as "Katyusha" ("Little Katya", similarly as how the German would call their "Dora" 800-millimeter super cannon) by the Russian soldiers and also by those who would suffer its deadly effects, consisted of a ramp of multiple rails (of variable number according to the type), installed in the box of a truck. The rails served as guide for a certain number of rocket projectiles propelled by solid fuel, capable of following a trajectory with a range of four to eight kilometers. The truck, generally a ZIS for the BM-8 and BM-13 (later the Studebaker supplied by the American would be used as well) and a GAZ for the BM-31, was one of three axes, with the driving cabin slightly armored and protected by some armored plates folded upon the roof, which were placed over the windscreen before opening fire. In the latest period of the war ramps installed in ZIS artillery tractors or in T-60 and T-70 light tanks were used as well. The BM were used as medium-caliber field artillery pieces, especially when it was necessary to achieve a strong saturation fire. Among other things, besides the notable devastating effect of these contraptions which were called "Stalin's organ" by the German, it should be considered as well the psychological and moral effect which they caused on the enemy soldier, who in a few seconds, and without expecting it, saw dozens of ululating rockets falling upon him, some of which carried, like the BM-13 illustrated in the picture, about 20 kilograms of explosive. During the war, also the American and the German would make use of rocket-propelled weapons. In fact the Wehrmacht would use them even before than the Red Army, and in many cases it would be a distinctly superior weapon, but they would be never used in mass numbers, and this way the effectiveness would be lost. Still some decades later, the Soviet Union and the countries of the Eastern Bloc had in service self-propelled rocket launcher vehicles which were heirs of those so rudimentary but effective contraptions which were heard for the first time in the battlefield the 15th July 1941.