MINE THROWERS & MORTARS

PART 3

47 mm - 60 mm mortars:

 

Captured 50 mm Soviet mortars "Naku"

50 Krh/38

(50mm mortar model 1938)

(50-PM 38)

PICTURE: Captured 50 Krh/38 mortar. (Photo taken in Sotamuseo). CLICK THUMBNAIL TO SEE LARGER PIC (145 KB).

Calibre:

50 mm

Barrel length:

78.0 cm

Weight in action:

12.1 kg

Muzzle velocity:

96 m/sec

Max. rate of fire:

30 shots / minute

Traverse:

6 degrees

Elevation:

fixed, 2 or 3 fixed settings:

45 degree setting (for distance of 800 meters)

75 degree setting (for distance of 400 meters)

82 degree setting (only in some, for distance of 100 m)

Min. range:

100 or 200 meters (depending if third elevation setting)

Max. range:

800 meters

Ammunition weight:

0.95 kg - 1.04 kg (with fuse)

Ammunition types:

HE

Country of origin:

Soviet Union

 

50 Krh/39

(50mm mortar model 1939)

(50-PM 39)

PICTURE: Captured Soviet 50 Krh/39 mortar in Finnish use. Photo taken in Kukkisjärvi October of 1941. (SA-kuva photo archive, photo number 61395). CLICK THUMBNAIL TO SEE LARGER PIC (174 KB).

Calibre:

50 mm

Barrel length:

77.5 cm

Weight in action:

14.0 kg (or 16.98 kg)

Muzzle velocity:

96 m/sec

Max. rate of fire:

30 shots / minute

Traverse:

6 - 15 degrees depending elevation

Elevation:

fixed, 2 or 3 fixed settings:

45 degree setting (for distance of 800 meters)

75 degree setting (for distance of 400 meters)

82 degree setting (only in some, for distance of 100 m)

Min. range:

100 or 200 meters (depending if third elevation setting)

Max. range:

800 meters

Ammunition weight:

0.95 kg - 1.04 kg (with fuse)

Ammunition types:

HE

Country of origin:

Soviet Union

 

50 Krh/40

(50 mm mortar model 1940)

(50-PM 40)

PICTURE: Captured 50 Krh/40 mortar. (Photo taken in Sotamuseo). CLICK THUMBNAIL TO SEE LARGER PIC (96 KB).

Calibre:

50 mm

Barrel length:

63.0 cm

Weight in action:

9.3 kg (and 12.1 kg while in carry)

Muzzle velocity:

96 m/sec

Max. rate of fire:

30 shots / minute

Traverse:

6 - 15 degrees depending elevation

Elevation:

fixed, 2 or 3 fixed settings:

45 degree setting (for distance of 800 meters)

75 degree setting (for distance of 400 meters)

82 degree setting (only in some, for distance of 100 m)

Min. range:

100 meters

Max. range:

800 meters

Ammunition weight:

0.95 kg - 1.04 kg (with fuse)

Ammunition types:

HE

Country of origin:

Soviet Union

 

Finnish use: 31 Soviet 50-mm mortars were captured and 15 of them re-issued to Finnish troops during Winter War. More than a thousand were captured during Continuation War (large majority of them in year 1941) and hundreds re-issued to Finnish infantry. Finnish military considered 50-mm weapons of nuisance, which were mainly suitable for harassing fire.

Development of light 50-mm mortars started in Soviet Union in year 1937. Soviet Red Army used them as company-level weapons - the Soviets divided their mortars as company (PM), battalion (BM) and regimental (HM) mortars. First model of these company mortars was 50-PM 38 (50-mm company mortar model 1938), which was approved to use of Red Army in year 1938 and entered production year later. However this first 50-mm mortar model was replaced in production still the same year with 50-PM 39 (50 mm company mortar model 1939), which was replaced in yet another model 50-PM 40 (50 mm company mortar model 1940) only few months later. Finally year 1941 also 50-PM 40 was replaced in production with yet new design, 50-PM 41 (50 mm company mortar model 1941), which remained in production until year 1943, when the Soviets decided to end manufacturing of 50-mm mortars. The reason for this was, that had reached the conclusion that mortar shells of calibre such a small calibre were not very effective and decided to concentrate their efforts in manufacturing larger mortars. Design-wise 50-mm mortars PM 38, PM 39 and PM 40 are all closely related (basically just slightly improved version of the one basic design developed after another), while PM-41 is quite different design, which has certain similarities with German 50-mm mortar, which may have effected to its development.

From these mortars PM 38, PM 39 and PM 40 were all based to basic Stokes structure - they had the usual barrel, base plate and bipod, but each of these designs had also some characteristics of their own. PM-38 had only two or three settings elevation settings, which were 45 degrees and 75 degrees (plus 82 degrees in some). The shooting distance was set with combination of either of these two settings and setting adjusted with slipping ring. This slipping ring placed around lower end of the barrel covered gas escape hole and by turning it soldier using the weapon could adjust the amount of explosion gases allowed to escape through the gas escape holes. Original Soviet mortar director used in 50-PM 38 was mechanical. This first Soviet 50-mm mortar proved to have more than its fair share of problems. From practical sense it was far too heavy and minimum shooting range (200 meters) was too long to be practical. Design-wise the mechanism of gas-escape system proved too complicated and its shooting range settings were false. Attachment of the mortar director was complicated and weak. The whole gas-escape was problematic as the hot gasses it released threw debris from the ground or could even hit the soldier using the mortar. PM 39 and PM 40 had not only improvements introduced to solve these problems, but also some improvements intended to make their mass-production easier and cheaper. Likely the most important of these manufacturing-related improvements were replacing original base plate and bipod designs with new parts, which were simple steel stampings. One of the main improvements of PM 39 was adding of protective shield, which directed the hot explosion gasses released from gas-escape system away from the soldier operating the mortar. While the Soviets manufactured variety of mortar directors for their 50-mm mortars the attachment for these remained rather weak. Each mortar of PM 38, PM 39 and PM 39 lineage also had shorter barrel, than its predecessor - probably to tackle the weight-issue. While 50-PM 38 had 78-cm barrel, PM 39 had slightly shorter 77.5 cm barrel and PM 40 only 63-cm barrel. As mentioned already Soviet 50-PM 41 had quite a lot in common with German 50-mm mortar of that time. Unlike earlier Soviet 50-mm mortars it did not have bipod, but relied to barrel yoke, which contained all traverse and elevation adjustments. It also had considerable changes to its gas-escape system, which now vented the gasses via tube under muzzle of the mortar.

During World War 2 all these 50-mm mortars were part of standard weaponry for Soviet Red Army and hence saw lot of use. Besides being common in Soviet use these mortars were also captured by German military in very large numbers and re-issued in wide scale to use of their military units. German military named captured Soviet 50-mm mortars in their use the following way:

While the Soviets did not use 50-mm mortars in combat after World War 2 they supplied these existing mortars to their allies. Both North Korea and North Vietnam used World War 2 era Soviet 50-mm mortars during Korean War and Vietnam War.

Finnish Army got its first experiences during Winter War (November 1939 - March 1940), during which 31 of these mortars were captured and 15 of them re-issued to use of Finnish units. The actual number of 50-mm mortars captured during Winter War was obviously much larger, but the wartime number does not include captured mortars, which were repaired to usable condition only after it or found only after the war among the melting snow. During Continuation War Finnish troops captured over thousand 50-mm mortars and they were re-issued to use Finnish Army in large numbers. As usual year 1941 with its Finnish advance and Soviet retreat was the time when most of them were captured. Large majority of these captured mortars seem to have been 50 Krh/39 (50-PM 39). According official tables of organisation and equipment by 1943 at least some of the Finnish infantry formations (such as Jaeger and Frontier Jaeger Battalions) received 50-mm mortars as part of their standard weaponry. But otherwise it seems that Finnish Army may have issued 50-mm mortars in less official manner - for example early June 1944 Finnish frontline troops had about third of them (about 400 mortars). But since they were not considered anywhere as useful as mortars in 81-mm - 82-mm calibre range, they did not replace anything and were typically used just for harassing the enemy by firing mortar shell or two every now and then. The accuracy however seems to have been relatively good - Finnish manual lists the scatter of shots from maximum range (800 meters) as 16 meters in length and 8 meters in width. Setting the mortar ready to fire was also very fast - this required only about a minute. The high-point for Soviet 50-mm mortars in Finnish inventory was in early June 1944 just before starting of Soviet offensives in Finnish front. At that time (1st of June 1944) Finnish Armed Forces had 1,225 captured Soviet 50-mm mortars, but less than one third of these (407 mortars) were issued to frontline troops. Summer of 1944 Soviet offensives in Carelian Isthmus and River Syväri / Svir forced Finnish troops to retreat until they succeeded stopping Soviet advance. During this phase of retreat lasting only few weeks Finnish troops suffered their largest losses of heavy weaponry and captured 50-mm mortars were no exception to this. That they saw quite a bit of use with Finnish troops during trench war period of Continuation War is visible from the fact that after Continuation War almost half of these mortars (590) were in need of repairs.

Losses of 50-mm mortars 9th of June - 7th of July 1944:

Unit:

Losses:

II Army Corps

0

III Army Corps

0

IV Army Corps

21

V Army Corps

24

Aunus Group

25

14th Division

0

Finnish Navy

0

Ladoga Coastal Brigade

0

Total:

70

Soviet 50-mm did not over impress Finnish soldiers. This also evidently effected to nicknames that Finnish soldiers assumed for Soviet 50-mm mortars - most common nickname was Naku (knock). Another less often used nickname used was Tiltu, which probably hinted similar attitude, as it was also the calling name for Finnish speaking Soviet female radio propaganda workers. While these mortars themselves were quite usable the ammunition used in them was relatively ineffective even in normal conditions - the mortar shells contained only about 100 grams of TNT, which was less than in some hand grenades. Deep snow muffled explosion of 50-mm mortar so effectively, that it made them basically harmless unless there was a direct hit. For this reason Finnish military did not really considered 50-mm mortars that important, even if they were captured in very large numbers. Instead of being effective weapons for inflicting casualties for infantry and destroying other soft targets they were considered nuisance weapons best suited for harassing the enemy. This also explains why Finnish Army re-issued them to use of own units in large scale during the trench war - they were cheap and easy to use weapons to normal rifle units of frontline infantry for lobbing occasional mortar shell to enemy trenches every now to for keep the enemy on his toes. But once the static trench war ended in June of 1944 they had less use. While single man could operate 50-mm mortar usually it had two-man crew. When the war ended captured Soviet 50-mm mortars were warehoused and along domestic 47-mm mortar prototypes they were declared obsolete in late 1950's. Year 1960 Finnish Defence Forces sold practically all remaining Soviet 50-mm mortars as scrap metal. From these 1,278 mortars sold as scrap metal 1,269 mortar and 15,000 mortar shells for them were sold to Interarmco. Only few of these mortars were retained for museum use.

Captured 50-mm Soviet mortars that Finland sold to Interarmco in year 1960:

mortar:

How many:

50 Krh/39

937

50 Krh/40

246

50 Krh/I

46

50 Krh/IV

34

50 Krh/II

5

Total:

1268

Notice: Certain mortar models listed here only with Latin numerals were versions of Soviet 50-mm mortar, which the Finnish military had failed to identify properly. Apparently these included model 1941 mortar, some Soviet 50-mm mortar models manufactured in small numbers (possible emergency production from year 1941) and/or prototypes.

When Finnish military re-issued 50-mm Soviet mortars they were first used with captured Soviet mortar shells. Once the number of captured mortar shells in Finnish inventory started declining to alarming level domestic manufacturer was needed for manufacturing more ammunition. This Finnish manufacturer was Högfors foundry, which manufactured 101,695 high-explosive mortar shells for captured Soviet 50-mm mortars in 1943 - 1944. From these 101,695 mortar shells 62,110 were manufactured year 1943 and 38,585 were manufactured in year 1944. Soviet 50-mm mortar shells contained basic propellant charge and had no additional propellant charges. This basic propellant charge (50 krh ppv in Finnish Army nomenclature) contained 4.5-grams of gunpowder. Soviet 50-mm mortar shells were transported in wooden boxes each containing 7 shells. Typically 8 such ammunition boxes were issued per mortar. Finnish Army mortars manuals list five models of captured Soviet 50-mm mortar shells, these were all high-explosive (HE) fragmentation type and are listed below.

name of mortar shell:

Weight (*):

shell length:

fuse:

# of secondary charges:

# of wings:

filled with:

country of origin:

50 tkr-4-V 27/30-M-50

735 g

17.0 cm

Soviet 27/30 M-50

none

4

TNT

Soviet Union

50 tkr-6-V 27/30-M-50

790 g

17.6 cm

Soviet 27/30 M-50

none

6

TNT

Soviet Union

50 tkr-6-V 27/40-M-1

790 g

17.6 cm

Soviet 36/40 M-1

none

6

TNT

Soviet Union

50 tkr-6-V 27/40-MP

790 g

17.6 cm

Soviet 36/40 MP

none

6

TNT

Soviet Union

50 tkr-4-V 36/40-M-1

790 g

17.6 cm

Soviet 36/40 M-1

none

4

TNT

Soviet Union

(*) Weight of mortar shell without fuse.

Because normal mortar shells of 50-mm mortar were so ineffective, during late Continuation War Finnish military attempted developing SRT-type "bouncing" mortar shell for these mortars. This kind of mortar shell would hit the ground, bounce back up and explode mid-air. At least in theory this explosion in suitable altitude would make the mortar shell much more lethal and this basic design had already proved successful with 81-mm mortar shells. But developing this type of special mortar shell in 50-mm calibre proved more difficult than anticipated. 2nd - 3rd of March 1944 Finnish military tested normal and SRT-type 50-mm mortar shells in winter conditions in Niinisalo test firing centre. In these tests target area had 50-cm (20 inch) of snow. The results indicated that the normal mortar shell exploded inside snow with barely visible results, while the bouncing shells exploded in height of 5 - 10 meters and fragmented well, but due to many shells exploding too high the effect in target was rather poor. It is unknown if SRT-type mortar shells for 50-mm mortars got to mass-production before ending of the war, but this seems unlikely.

Soviet 50-mm mortar shell also was a tool in grim record of sort during Continuation War. Summer of 1944 Private Hugo Turunen serving 14th Division became what was likely a rather questionably lucky record holder of Finnish Army in series "survivor from direct hit with ordnance of largest calibre". Soviet 50-mm mortar shell hit him in the upper back and slid under his skin until it stopped just on top his left buttock. While he was unlucky to be hit in the first place he had incredibly good luck in the sense that the mortar shell didnít explode and was successfully removed in operation done in nearest field hospital.

 

OTHER MORTARS OF 47MM - 60MM USED BY FINNISH ARMY:

PICTURE: One of the pre World War 2 Tampella 47-mm mortar prototypes. This particular prototype is version 35a of second prototype (manufactured year 1935). Notice direct fire sights on this mortar. CLICK THUMBNAIL TO SEE LARGER PIC (117 KB).

PICTURE: Two versions of mortar shells used with Tampella 47-mm mortars developed in 1930's. This ammunition design was basically Finnish M/32 egg hand grenade equipped with tail-section and suitable concussion fuse. CLICK THUMBNAIL TO SEE LARGER PIC (88 KB).

- 47-mm Tampella Mortars (mainly 47 Krh/39): Before World War Tampella was developing 47-mm domestic mortar, which could be carried by one man. The development started from 60-mm mortar prototype, which Tampella designed in year 1934. First 47-mm prototype (called 47 Krh/35) was based to ideas of engineer Leo Jyväkorpi and manufactured in spring of 1935. This first prototype had gas-escape system, which was used for adjusting firing distance, while later versions had adjustable breech, which was adjusted with cogwheel like mechanism. These mortars were able to fire 20 - 40 mortar shells per minute to maximum distance of 750 meters. The mortar shells used in them were simply Finnish m/32 egg hand grenades equipped with tail units and concussion fuses. The tail units used contained integral primary propellant charge. Finnish m/32 egg hand grenade was offensive hand grenade, which was manufactured in two versions - symmetrical and elliptic. Both of these versions could be used in mortar shells. Development of 47-mm mortars continued in Tampella until year 1939. The final (sixth) prototype version was manufactured year 1938 and Finnish Army ordered six of these prototypes for field tests. Tampella manufactured this field test series of six mortars and delivered them to Finnish Army, which named them 47 Krh/39 (47 mm mortar model 1939). There is reason to believe these six field test series mortars saw frontline use during Winter War. 24th of January 1938 Finnish Army was testing new fuses of 47-mm fuses in live fire testing range in Harakka Island when faulty fuse caused mortar shell to explode immediately after exiting barrel. The explosion killed Inspector of Infantry Major General A.S. Heikinheimo and wounded four others, two of them (Engineer Leo Jyväkorpi and Major Ahonen) seriously. Unlike claimed by some sources, this accident doesn't seem to have stopped development of 47-mm Tampella mortars, but the large number of captured Soviet 50-mm mortars made their further development and manufacturing unnecessary.

PICTURE: 47 Krh/41 mortar propped ready to fire. (Photo taken in Sotamuseo). CLICK THUMBNAIL TO SEE LARGER PIC (67 KB).

- 47 Krh/41 (47 mm mortar model 1941): Year 1942 Finnish company Oy Santasalo-Sohlberg Ab manufactured 50 of these 47-mm mortars to Finnish Army. This production run could most likely be best considered as large-scale field test series. 47 Krh/41 weight 3.2-kg and had three elevation settings - 45 degrees, 65 degrees and 75 degrees. Minimum shooting range was only 35 meters and maximum shooting range 170 meters. It is worth nothing that this mortar did not use the same ammunition as Tampella's 47-mm mortars. Instead it had its own kind of specific 650-gram weighting mortar shell resembling Finnish M/41 egg hand grenade. As a propellant charge this mortar shell used normal 7.62 mm x 54R rifle/machinegun cartridge. This mortar shell contained 70 grams of TNT and produced some 250 - 300 steel fragments, which from 2.5-meter distance were able to penetrate inch-thick pine plank with ease. Early on these mortar shells were equipped with fuse of Finnish M/32 egg hand grenade, which was set off by impact and detonated after 5.5-second delay. Later on they were equipped with specially made fuses, which provided 7.5 - 8 second delay. Mortar shells were delivered in boxes of 10 shells, each of these boxes weighting about 10-kg. The whole mortar was also only 61.8-cm long, it had integrated folding bipod and could easily be carried by one man. For this purpose it had a carrying sling made from leather. Range adjustment system used in it was a gas-escape system. The gas-escape system had an adjustment ring aka "firing distance drum", adjusting which controlled the amount of propellant gasses released. Wartime test firing revealed the time delay fuses after some practice allowed mortar shells be fired so, that they exploded mid-air over targets (for maximum damage). However soldier firing the mortar had to remember keeping his distance - otherwise the hot and high-pressure propellant gasses released by gas-escape system might hit his face and eyes. According reports delivered to Finnish Army Ordnance Department most of these mortars were issued to frontline units and presumably saw combat use in 1942 - 1944.

PICTURE: 47 Krh/41 mortar set ready for carry. As seen in this photo equipment of this mortar included rifle-sling like leather sling, which allowed one soldier to carry the mortar easily for long distances if needed. CLICK THUMBNAIL TO SEE LARGER PIC (67 KB).

- 47 GrK m/40 (Swedish 47 mm mortar 1940): Few of these Swedish 47-mm mortars were field tested in Swedish volunteer Battalion (Svenska Frivilling Bataljonen - SFB) of Finnish Army in year 1941, when the battalion took part in battles of Hanko Peninsula. This mortar was manufactured by Tönseth & Co Ab. Weight of the complete weapon 11.7-kg (mortar barrel 2.9-kg, bipod-mount 6.5-kg and base-plate 2.3 kg). Shooting range 100 - 480 meters. This mortar was introduced to use of Swedish Army in year 1941 and remained in its use until about year 1950.

- 60 mm Brandt mortar: When Winter War started in November of 1939 Finnish Army confiscated all mortars that Tampella had manufactured for Brandt, but had not yet delivered. Among these confiscated mortars were some 60-mm Brandt mortars, which may have seen training use in home front during Winter War. Finnish ammunition production for 60-mm mortars doesn't seem to have existed and as far as known no ammunition for them was imported either.

 


Source materials used for making these mortar pages listed on bottom of MINETHROWERS AND MORTARS PART 7.

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