152 mm howitzer M1938 (M-10)

152 mm howitzer M1938 (M 10) (152 мм гаубица обр. 1938 г. (М 10)) was a Soviet 152.4 mm (6 inch) howitzer of World War II era. It was developed in 1937–1938 at the Motovilikha Mechanical Plant by a team headed by F. F. Petrov. Although production of the gun was stopped in 1941, it saw combat with the Red Army until the end of World War II and remained in service until the 1950s. Captured pieces were used by Wehrmacht and the Finnish Army. The latter kept the M 10 in service until 2000. In a tank mounted variant, M 10T, the gun was mounted on the KV 2 heavy tank.

By the early 1930s the Red Army (RKKA) started to look for a replacement for the 152 mm howitzer M1909 and the 152 mm howitzer M1910. Those pieces, developed before World War I, had unsprung fixed trail carriages and short barrels, which meant poor mobility, insufficient elevation and traverse angles and short range. Although both pieces were eventually modernized, resulting in the 152 mm howitzer M1909/30 and the 152 mm howitzer M1910/37 respectively, these were relatively minor upgrades which brought only limited improvement in some areas and didn't address others. It was clear that a completely new design was needed. However, at that time, the Soviets had little experience in developing modern artillery pieces. An initial attempt was made to overcome that issue through a collaboration with Germany. Constrained by the limitations of the Treaty of Versailles, Germany was looking for ways to proceed with weapons development and joint projects gave them such an opportunity. Among other weapons supplied by Germans was a heavy howitzer, designated 152 mm howitzer M1931 (NG) in the USSR. Soon the Motovilikha Mechanical Plant (MMZ) was tasked with the production of this gun. However, only eight pieces were completed in 1932–1934 until production was stopped. The design proved to be too complicated for the Soviet industry of the early 1930s, similar to other designs like 122 mm howitzer M1934 or 20 mm and 37 mm autocannons. Also it was considered somewhat heavy at 5,445 kg in travelling configuration. But these early failures gave Soviet developers some valuable experience. In 1937, F. F. Petrov and his design team at the Plant No.172 (another name for Motovilikha Plant) started work on a new design, the M 10. Technical papers were submitted to the Artillery Directorate on 1 August 1937 and on 2 November the first prototype was completed. Ground trials (19–25 October 1938) featured two pieces: No. 302 (L/25 barrel with constant rifling) and No. 303 (L/20 barrel with progressive rifling). The No. 303 was found to be superior. The trials also revealed numerous defects in the gun construction: the howitzer suffered from insufficient upper carriage strength, leaks in the recoil buffer, unreliable suspension etc. For army tests early in 1939, an improved design with a longer barrel was presented. Another series of army tests followed from 22 December 1939 to 10 January 1940, but even before it started—on 29 September 1939—the gun was adopted as 152 mm divisional howitzer model 1938. Later, the word divisional was removed from the designation.

The M 10 was much more advanced design compared to older Soviet 152 mm howitzers. It had a modern split trail carriage which allowed for a much larger traverse. The trails were of riveted construction. The carriage was equipped with suspension and wheels from the ZiS 5, increasing towing speed. The barrel, much longer than that of older designs, was fitted with an interrupted screw breechblock with recoil devices consisting of a hydraulic recoil buffer and hydro pneumatic recuperator. The recoil travel was variable. A gun shield provided some protection from bullets and shell fragments. Unlike its eventual successor, the D 1, the M 10 was not equipped with a muzzle brake. While softening recoil and thus allowing for a lighter carriage, a muzzle brake has the disadvantage of redirecting some of the gases that escape the barrel toward the ground where they raise dust, revealing the gun position. The gun could be towed by an artillery tractor or a team of horses. In the latter case, a 400 kg limber was used.

In addition to the towed howitzer, a vehicle mounted variant was developed for use in KV 2 heavy tanks. This variant—152 mm tank howitzer M1938 (M 10T)—had a shorter barrel. A single prototype with powder bag loading was built in 1939.

The M 10 project provided the RKKA corps artillery with a modern 152 mm howitzer, which combined good firepower with good mobility (although, as the example of the D 1 shows, the latter characteristic could be improved without compromising the former). When compared to a typical contemporary howitzer of similar calibre, the M 10 had shorter range, but was lighter. E. g. the German 15 cm sFH 18 had a range of 13,325 m—about one kilometer longer than that of the M 10—but also weighed much more (5,510 kg in traveling position). The same can be said about the US 155 mm howitzer M1 (14,600 m, 5,800 kg) or 149 mm howitzer manufactured by the Italian Ansaldo (14,250 m, 5,500 kg). A German howitzer with characteristics similar to those of the Soviet one—the 15 cm sFH 36—didn't reach mass production. Compared to older pieces such as the French Schneider model 1917 (11,200 m, 4,300 kg), the M 10 had advantage in range and comparable weight.

The M 10 used separate loading ammunition, with eight different charges. The charges ranges from the "full charge" Zh 536 and smaller charges ranging from the "first" to "sixth", which was the smallest. A "special charge" was used with the BP 540 HEAT projectile. Propellant charges were produced in "full" and "third" variants in munitions factories. All other charges were derived from removing small gunpowder bags from the charge cartridge. For flash suppression there was a special chemical mixture which was inserted into cartridges before night firing. 152 mm projectiles for the M 10 weighed about 40 kg, making a difficult job for loaders, who had to carry the projectiles alone. When set to fragmentation mode, the OF 530 projectile produced fragments which covered an area 70 meters wide and 30 meters deep. When set to high explosive (HE) action, the exploding shell produced a crater about 3.5 meters in diameter and about 1.2 meters deep. The OF 530 is still fired from modern 152 mm ordnance pieces of the Russian Army. The G 530 HEAC anti concrete shell had a muzzle velocity of 457 m/s when fired with the "first" charge. At a range of one kilometer it had 358 m/s terminal velocity and was able to punch through up to 80 centimeters of reinforced concrete before detonating a TNT charge which increased the total penetration to 114 centimeters. The G 530 could not be fired with a "full" charge without putting the crew at risk of having the shell explode in the barrel. A special version of the shell, the G 530Sh, was developed to allow use with the full charge. The BP 540 HEAT projectile was not used during World War II. It had an armour penetration of 250 millimeters at an incident angle of 90°, 220 millimeters at 60°, 120 millimeters at 30°. Available ammunition Type Model Weight, kg HE weight, kg Muzzle velocity, m/s Range, m Armor piercing shells Naval semi AP model 1915/28 51.07 3.2 HEAT BP 540 27.44 Anti concrete shells Anti concrete shell G 530 / G 530Sh 40.0 5.1 High explosive and fragmentation shells HE Fragmentation, steel OF 530 40.0 5.47–6.86 HE Fragmentation, steely iron OF 530A 40.0 5.66 HE, old F 533 40.41 8.0 HE, old F 533K 40.68 7.3 HE, old F 533N 41.0 7.3 HE, old F 533U 40.8 8.8 HE, steely iron, old French F 534F 41.1 3.9 HE for 152 mm mortar model 1931 F 521 41.7 7.7 HE, British, for Vickers 152 mm howitzer F 531 44.91 5.7 Shrapnel shells Shrapnel with 45 sec. tube Sh 501 41.16–41.83 0.5 (680–690 bullets) Shrapnel with Т 6 tube Sh 501T 41.16 0.5 (680–690 bullets) Illumination shells Illumination, 40 sec. S 1 40.2 Chemical shells Chemical howitzer shell HS 530 38.8 Chemical howitzer shell HN 530 39.1 Chemical (post war) ZHZ