152 mm howitzer - gun M1937 ( ML - 20 ) The 152 mm howitzer - gun M1937 ( ML - 20 ) ( ) , was a Soviet gun - howitzer . The gun was developed by the design bureau of the plant no 172 , headed by F . F . Petrov , as a deep upgrade of the 152 - mm gun M1910 / 34 , in turn based on the 152 - mm siege gun M1910 , a pre - World War I design by Schneider . It was in production from 1937 to 1946 . The ML - 20 saw action in World War II , mainly as a corps / army level artillery piece of the Soviet Army . Captured guns were employed by Wehrmacht and the Finnish Army . Post World War II , the ML - 20 saw combat in numerous conflicts during the mid to late twentieth century . Description . The ML - 20 was officially classified as howitzer - gun , i . e . an artillery system which combines characteristics of a howitzer and ( to lesser extent ) of a gun and therefore can be used in both roles . This universality was achieved by wide range of elevation angles and by using separate loading with 13 different propellant loads . The gun was fitted with both telescopic sight for direct fire and panoramic sight for an indirect one . For ballistic calculations and meteorological corrections a special mechanical device was developed . The device , called " meteoballistic summator " , consisted of a specialized slide rule and a pre - calculated table . After World War II similar devices were introduced for other types of guns . The barrel was either monobloc or built - up . Some sources indicate that a third type - with loose liner - also existed . To soften recoil , a large slotted muzzle brake was fitted . The breechblock was of interrupted screw type , with forced extraction of cartridge during opening . A safety lock prevented opening of the breechblock before the shot ; if there was a need to remove a shell , the lock had to be disabled . To assist loading when the barrel was set to high elevation angle , the breach was equipped with cartridge holding mechanism . The gun was fired by pulling a trigger cord . The recoil system consisted of a hydraulic buffer and hydropneumatic recuperator . Each held 22 litres of liquid . Pressure in the recuperator reached 45 atm . The carriage was of split trail type , with shield and balancing mechanism , leaf spring suspension and steel wheels with rubber tire s ( some early production pieces received spoked wheels with solid tires from M1910 / 34 ) . During transportation the barrel was usually retracted . The gun could also be towed with the barrel in its normal position , but in this case the transportation speed was limited , about 4 – 5 km / h ( compared to 20 km / h with barrel pulled back ) . The gun could be set up for combat in 8 – 10 minutes . The carriage , designated " 52 - L - 504A " , was also used in the 122 - mm gun model 1931 / 37 ( A - 19 ) . Development history . Among other artillery pieces the Red Army ( RKKA ) inherited from the Imperial Russian Army a 152 - mm siege gun M1910 , developed by Schneider . The gun was modernized twice in 1930s , resulting in the 152 - mm gun M1910 / 30 and the 152 - mm gun M1910 / 34 . However , its mobility , maximum elevation and speed of traverse still needed improvement . In 1935 - 36 the No . 172 Plant in Motovilikha tried to continue the modernization works , but the Main Artillery Directorate ( GAU ) insisted on more significant upgrade . Consequently , the design bureau of the plant developed two guns ML - 15 and ML - 20 . While the former project was initiated by GAU , the latter started as private development ; the team working on it was led by F . F . Petrov . Both guns used barrel and recoil system of the M1910 / 34 . The ML - 20 also inherithed from the older gun its wheels , suspension and trails . The ML - 15 reached ground tests in April 1936 , was returned for revision and was tested again in March 1937 , this time successfully . The ML - 20 went through ground tests in December 1936 and through army tests next year . After some defects ( mostly in carriage ) were eliminated , the ML - 20 was recommended for production and on 22 September 1937 it was adopted as 152 - mm howitzer - gun model 1937 ( ) . It is not clear why the ML - 20 was preferred . The ML - 15 was lighter ( about 500 kg less in combat position , 600 kg in traveling position ) and more mobile ( maximum transportation speed 45 km / h ) . On the negative side , the ML - 15 had more sophisticated carriage ( however , the final version of the ML - 20 carriage incorporated some features of the ML - 15 ) . Some sources claim that the choice was made because of the economic factor - the ML - 20 was more similar to the M1910 / 34 , meaning less arrangements for production . Production history . The gun was in production in 1937 - 46 . 6 , 884 guns were manufactured and about 4 , 000 ML - 20S barrels for using in self - propelled gun s SU - 152 and ISU - 152 . The ML - 20 was eventually replaced by the D - 20 152 mm gun with identical ballistics , which entered production in 1956 . Smaller production rates toward the end of the war were caused by two reasons . First , most of the barrels produced in these years were ML - 20S . Second , after Germans fielded heavy tanks the plant was ordered to increase production of A - 19 122 mm guns instead of some ML - 20 . Organization and employment . Red Army . The ML - 20 was originally intended for corps artillery . Together with the 122 - mm gun A - 19 it formed a so - called " corps duplex " . In 1940 - 41 there were three types of corps artillery regiment s : Soon after the outbreak of Operation Barbarossa , the corps artillery was eliminated ( as rifle corps themselves were eliminated ) . It was restored later in the war . The new corps artillery regiments were supposed to be armed with 122 - mm guns or 152 - mm howitzers , but some memoirs mention that the ML - 20 was also used . From 1943 the gun was employed by artillery regiments of armies . Such regiment had 18 ML - 20s . Guard armies from early 1945 had artillery brigade with 36 ML - 20s . The ML - 20 also used by artillery regiments ( 24 pieces ) and brigades ( 36 pieces ) of the Reserve of the Main Command . It was primarily used for indirect fire against enemy personnel , fortification s and key objects in the near rear . Heavy fragments of the OF - 540 HE - Fragmentation shell were capable of piercing armour up to 20 – 30 mm thick , making a barrage dangerous to thinly armored vehicles and to some extent to heavier armoured ones as the fragments could damage chassis , sights or other elements ; sometimes a close expolsion caused damage inside a vehicle even though the armour remained intact . Direct hit of a shell often resulted in tearing away a turret of a medium tank or jamming it in case of a heavy tank . The gun was also equipped with armour - piercing shells for direct fire against armoured targets . Although not an ideal anti - tank gun because of its large size , slow traverse and slow rate of fire , in 1943 the ML - 20 was one of a few guns effective against new German tanks . For example , the glacis armour of the heavy Tiger I could be penetrated from about a kilometer . The first combat use of the ML - 20 was in the Battle of Khalkhin Gol , in limited numbers . It also saw combat in the Winter War against the Mannerheim Line fortifications . The gun proceeded to be used throughout the second world war . Excellent characteristics of the gun , including reliability and ease of maintenance , allowed it to remain in service with the Soviet Army for a long time after the war . Other operators . In the early stage of the German invasion of the Soviet Union hundreds of ML - 20 were captured by Wehrmacht . The gun was adopted by Germans as 15 . 2 cm KH . 433 / 1 ( r ) . From February 1943 Germans manufactured an ammunition for the gun . The Finnish Army captured 37 guns of the type in 1941 - 44 and received additional 27 from Germany . These guns were adopted as 152 H 37 . A number of barrels were mated with carriages of A - 19 to create 152 H 37 - 31 . While the gun was generally liked , the Finnish Army didn ' t possess enough prime movers suitable for towing such a massive piece . As a result , some of the guns were assigned to coastal artillery . Two pieces were captured back by the Red Army . A number of these guns were modernized in 1988 and as of 2004 still remain in reserve as 152 H 88 - 37 . ( all of the 152 H 88 series are being withdrawn as of 2007 ) . After the war the ML - 20 was widely exported to Warsaw Pact allies and to many states in Asia and Africa ( in some of those states the gun still remains in service ) . It was adopted by Egypt and Syria and therefore saw action in Arab - Israeli conflict . In 2002 a TV documentary featured ML - 20 employed by the Afghan Northern Alliance forces against the Taliban fighters ; it seems likely that the guns were initially supplied to the Najibullah ' s regime . Variants . The barrel was manufactured in two variants - monobloc or built - up . Some sources indicate that a third type - with loose liner - also existed . Except the basic variant , the only variant to reach mass production was the ML - 20S , developed for use in self - propelled guns , with differently placed controls for easier operation in small enclosed compartment . Summary . The ML - 20 was one of the most successful Soviet artillery pieces of World War II . Its characteristics positioned it between classical short - range howitzers and special long - range guns . Compared to the former , the ML - 20 has better range ( e . g . the German 15 cm sFH 18 had range of 13 . 3 km ) , which often allowed it to shell positions of enemy artillery while remaining immune to enemy fire . Its advantage over the latter was in weight and cost , and therefore in mobility and production rate . For example , the German 15 cm K 39 with range of 24 . 7 km weighed 12 . 2 tons and only 61 pieces were built ; of the excellent 17 cm K 18 ( 23 . 4 t , 29 . 6 km ) 338 pieces were manufactured ; lighter 10 . 5 cm sK 18 ( 5 . 6 t , 19 . 1 km ) was more common ( 2 , 135 pieces ) but its 15 kg shell was much less powerful than a 44 kg shell of ML - 20 . German attempts to produce an analogue to the ML - 20 were unsuccessful . The 15 cm sFH 40 was never produced due to construction defects ; the 15 сm sFH 42 had insufficient range and only 46 pieces were built . In 1943 and 1944 Wehrmacht announced requirements for a 15 cm howitzer with a range of 18 km , but none reached production . Of other guns with more or less similar characteristics , there were French 155 mm guns model 1917 and 1918 with longer range , but some 3 . 5 tons heavier ( as was the US 155 mm Long Tom ) . The Czechoslovakian howitzer K4 ( used by Germans as 15 cm sFH 37 ( t ) ) was about 2 tons lighter , but with range more than 2 km shorter and only 178 pieces were built . The British BL 5 . 5 inch ( 140 mm ) Medium Gun probably had the closest characteristics ; weight slightly over six tons and range of with an shell . The main shortcomings of the ML - 20 were its weight and limited mobility . As the experience of the ML - 15 project suggests , the gun could be made somewhat lighter and more suitable for high - speed transportation . The use of a muzzle brake can be seen as a minor flaw : while softening the recoil and thus allowing the use of a lighter carriage , a muzzle brake has the disadvantage of redirecting some of the gases that escape the barrel toward the ground , where they can raise dust , potentially revealing the gun position . But when the ML - 20 was developed , muzzle brakes were already a common design element in artillery pieces of that class . Surviving pieces . ML - 20s are on display in a number of military museums . Among other places , the gun can be seen :