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LPP-25: Light, Simple, and Unwanted

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The light LPP-25 anti-tank gun was built as an answer to the German s.Pz.B.41 anti-tank rifle. As a result of information that reached Soviet designers from the front lines, a weapon was born that did not lose out to the German gun, but without the complex and short-lived conical barrel. What was this LPP-25 like?


The idea of a light anti-tank gun with high penetration was born in the Dzerzhinskiy Artillery Academy in the spring of 1942, when its lecturers learned of light and effective German anti-tank weapons. This information was combined with information about massed use of fast tanks, assault guns, and armoured cars with, at the very least, bulletproof armour, and the theories of the lecturers about the use of anti-tank guns in battle.

Ambitious plans

The academy's students and most of the teachers were sent to the front lines. The academy itself was evacuated to Samarkand in mid-November of 1941. The remaining teachers did not lose contact with their former students and colleagues, and proposed a new weapon based on correspondence with th front lines.

Drawing of the LPP-25 type 1, travel position.

Anti-tank guns were the main method of dealing with tanks and armoured cars. They were very effective during defenses when firing from prepared positions, but needed tractors during an offensive to keep up with tanks and infantry. If the enemy counterattacked, they did not have time to prepare convenient positions. For these reasons, the use of anti-tank rifles to reinforce infantry units on the defensive and during an offensive was considered optimal. These rifles had a number of advantages: they were light, small, and had good penetration at short range. At the same time, they had their drawbacks: heavy weight for only one soldier, difficulty in aiming at moving targets, insufficient penetration at ranges past 300 meters.

As a result, a project was created to plug the gap between an anti-tank rifle and a medium anti-tank gun: a light anti-tank gun, capable of keeping up with infantry. The main opponent of this gun would be light and medium tanks, armoured cars, regular cars, and enemy strongholds. The larger caliber would improve penetration and the mount would make it easier to aim at moving targets. The s.Pz.B.41 conical barreled anti-tank rifle influenced the development, as it was ideal for that role.

The project's main author was Engineer-Lieutenant-Colonel A.N. Sidorenko. Engineer-Captain M.F. Samusenko and Engineer-Captain I.I. Zhukov worked alongside him. They composed tactical-technical requirements for a weapon which was presented to the department of artillery. After a long discussion, work on the project was approved.

Drawing of the LPP-25 type 1, battle position.

The 25 mm caliber was chosen for the gun, as it was optimal from the point of view of compactness and overall weight, but allowed for penetration of over 35 mm of armour. The gun was designed to use as many parts from guns that were currently in production as possible.

The ammunition was new, but made with existing components. The 295 g AP shell was taken from the 25 mm AA autocannon mod. 1940, and the casing was a necked-down version of the 37 mm mod. 1930's round. The muzzle velocity of 1200 m/s was expected. The overall weight of the gun was limited to 230 kg.

Seems that the designers of the project, indexed LPP-25, had the opportunity to familiarize themselves with the ammunition for the s.Pz.B.41, and not just the gun itself. A special 25 mm shell with a tungsten core was proposed, similar in size to the one in the German shell. The argument was that the USSR already produced tungsten cores for 12.7 mm bullets and a slightly larger core would not be an issue. The mass of such a shell was 200 grams, and the muzzle velocity would increase to 1400 m/s.

Barrel of the anti-tank gun.

Since the tungsten core shell would be expensive to produce, it was assumed that the ammunition loadout would contain no more than 25% of these shells and that they would be used only in special circumstances, such as when enemy heavy tanks appeared less than 300 meters away and all regular shells were expended.

Calculations were also done for a shell analogous to the German s.Pz.B.41. In this case, the muzzle velocity increased to 1700 m/s and the penetration would have been 1.5 times higher. The calculated penetration of the LTT-25 with any shell was higher than that of its German equivalent.

The barrel and breech of the gun were developed in April of 1942. The overall project was finished and approved in May, at a special meeting with the academy's dean. After that, the blueprints were passed on to the People's Commissariat of Armament for production.

The barrel and breech were built at the Molotov factory #172 in Motoviliha, a suburb of Molotov (within modern day Perm). Since the factory was busy with production of the 45 mm mod. 1937 gun and tasks connected with the M-42 and M-6 guns, it took some time to fulfill the academy's request. Only a long string of letters and personal involvement of GKO member L.P. Beria in October of 1942 managed to get two barrels and two breeches produced and sent to factory #702 in Tashkent.

Left: the shell from the 25 mm mod. 1940 AA autocannon in the shell casing from the 37 mm AT gun mod. 1930. Right: LPP-25 type 1 AT gun in travel and battle position.

Factory #702 developed working blueprints and assembled two experimental prototypes on different mounts and with different barrels. Some parts were built by warehouse #20 in Tashkent. Thorough cooperation was required, and production was faced with many difficulties, mostly because of lack of communication. This delayed production.

Both guns were delivered to the academy in January of 1943. A commission inspected the prototypes on January 30th and tried out the first prototype. Due to a lack of an artillery proving grounds or proper gunpowder, a limited amount of trials was performed.

Calculated penetration of the LPP-25 depending on distance and angle of armour:


LPP-25

s.Pz.B.41


1

2

3

Angle

90

60

90

60

90

60

100 m

73

53

105

78

Up to 75

45-50

400 m

62.3

44.8

82

57

40

-

500 m

59.3

42.7

76

54

-

25

600 m

55

40.4

-

-

-

-


Variant 1: steel shell, V₀ = 1200 m/s, mass = 295 g
Variant 2: special shell, V₀ =1400 m/s, mass = 200 g
Variant 3: special shell 28/20, V₀ = 1360 m/s, mass = 123 g

Description of the LPP-25 type 1 anti-tank gun

  • Caliber: 25 mm
  • Practical rate of fire: 20-25 RPM
  • Vertical range: -7 to +11 degrees
  • Horizontal range: 30 degrees
  • Aiming speed: 
    • Horizontal: 6° per second
    • Vertical: 2°24' per second
  • Bore axis height: 300 mm
  • Clearance: 300 mm
  • Wheel base: 1080 mm
  • Mass: 240 kg
  • Time to convert from travel to battle position: 8-10 seconds
  • Dimensions in travel position, LxWxH: 3500x1250x1060 mm
  • Dimensions in battle position, LxWxH: 3300x2020x800 mm
  • Top speed: 60 kph
  • Number of parts without wheels or sight: 402, 32 of which are borrowed from other designs
The gun was made up of five assemblies:
  • Oscillating part
  • Upper mount with elevation and turning mechanism
  • Lower mount with wheels, suspension, and trails
  • Shield
  • Optical sight
The oscillating part included the cradle, recoil brake, monobloc barrel with 12 rifling grooves (34 caliber twist), 2525 mm in length (L/101), connected with the breech, the direction case, the retaining nut, return mechanism, and muzzle brake. The breech was taken from the 37 mm AA autocannon mod. 1937 with some minor changes.


Conversion of the LPP-25 from battle position to travel position. The project's authors are likely pictured.

The upper mount contained the elevation and horizontal traverse mechanisms, which were similar in design to "classical" anti-tank guns.

The pipe-like trails with travel locks were attached to the lower mount with ball joints. The lower mount was built as a platform with the wheels, suspension, and trails.

The wheels deserve special attention. Mounted on a cranked axle with a winch and leaf springs, they were taken from the TIZ AM-600 motorcycle, but with a solid tire. The shape of the axle raised the wheels in battle position, and the lower mount rested on the ground on a special spade.

The shield was 3 mm thick, had an irregular shape, and was sloped at 30 degrees. The shield was designed to protect the crew from pistol caliber bullets and light shrapnel. The shield could not deflect a rifle bullet at close range.

Aiming flywheels of the LPP-25 type 1.

The "duck" type optical sight was original, and had 3x magnification and a FOV of 12 degrees. It was designed to fire at a range of up to 1000 meters without raising the gun.

Firing trials showed that the muzzle velocity was less than calculated: 1165-1180 m/s instead of 1200. Nine shots were fired at the 465. mm rear hatch of a T-34 from 140 meters at 90 degrees. Two hits registered, one in the side, making a penetration with a fragment knocked out, one in the center, making a clean penetration.

It turned out that the muzzle brake, designed like the German s.Pz.B.41 muzzle brake, was too effective, at three times better than calculated. This caused short recoils, and the semiautomatic mechanism either worked poorly or not at all. The muzzle brake was safe and did not stun the gun crew. It was decided that using this muzzle brake design on other guns was reasonable.

Rear hatch from a T-34 tank after being shot with the LPP-25 gun.

The gun turned out to be stable when firing with the barrel in any position. This was achieved because the mount rested on the ground in battle position.

The gun was easy to move across cross-country terrain with the strength of the crew alone. The small weight and size allowed it to fit inside the truck bed of a ZIS-5 truck and many others. A proposal was made to simplify the design by removing the suspension. That way the gun could fire from its wheels.

LPP-25 anti-tank gun, type 2

The second variant of the gun had significant differences. The barrel, designed for shells with a muzzle velocity of 1400 m/s, had its rifling twist at 45 calibers, as opposed to 34 calibers with the first type of gun. There was no traverse mechanism. Aiming was done in the same way as on the s.Pz.B.41, with the gunner's right hand pulling on a handle attached to the cradle. The handle also housed the firing mechanism. A ribbon brake was used to regulate the aiming sensitivity which was used for precise aiming (for example, at the firing port of a pillbox).

The shield attachment was simplified. The wheels were removable, and had handles for transport. The box-like trails were similar to early s.Pz.B.41 trails. The optical sight was different, the PP-9 model.

LPP-25 type 2 in battle and travel positions.

The LPP-25 type 2 was assembled from 375 parts, not counting the sight or wheels, 32 of which were already in mass production.

After trials, the academy commission concluded that the LPP-25 was a modern artillery system that could become a good anti-tank gun to support infantry and tanks. The commission concluded that the gun could be installed on an SPG, used in airborne units, was simple and safe to use, and had significant reserves for simplification. The ammunition could be put into mass production quickly. The commission deemed it necessary to send the gun to proving grounds trials.

Trials

On February 6th, 1943, the dean of the Artillery Academy, Major-General S.P. Sidorov, sent documents regarding the design and trials of the LPP-25 to the Deputy People' Commissar of Defense, Marshal of Artillery N.N. Voronov and GAU Chief Colonel-General N.D. Yakovlev with a request to perform trials.

On March 30th, 1943, a decision was made by the Chief of Staff of Artillery, Major-General of Artillery F.A. Samsonov, that if the drawbacks of the LPP-25 were resolved, it could be accepted as battalion or even regimental level artillery.

The LPP-25 began trials at the Gorohovets proving grounds in early July of 1943. Three types of shells were made: light subcaliber (163 grams), regular steel, and a tungsten core round.

Firing from the LPP-25 type 1.

Aside from trials against armoured plates and stability trials, the light subcaliber shell was used against a captured German tank "medium in weight and heavy in armament" (likely a PzKpfw III) from a range of 100 meters. The gun was aimed at the 45 mm thick upper and lower front plates. The results were all complete penetrations.

However, not all calculations were correct. For example, it took 20-30 seconds to convert the type 1 gun into battle position, and 26-45 seconds to convert it back. The mass was also a bit higher than expected at 277 kg. The width of the shield was insufficient, it was uncomfortable to aim, a lack of recoil guard meant that the crew could sustain injury when firing, and the sight markings were poor.

A number of improvements followed, including the gun shield.

The second round of trials took place during September and November of 1943. The trials found the type 1 gun superior, under the condition that newfound defects be resolved.

Improved gun shield for the LPP-25 type 2.

The penetration of the LPP-25 was established as follows:
  • The stock AP-T shell from the 25 mm AA autocannon mod. 1940 (286 g) penetrated 45 mm of armour at 60 degrees from a range of 340 m.
  • The experimental light subcaliber shell, German type (167 g) could penetrate 60 mm of armour at 60 degrees from 500 meters, 75 mm of armour at 60 degrees from 65 meters, and 90 mm of armour at 90 degrees from 200 meters.
  • The experimental subcaliber shell from the 25 mm AA autocannon mod. 1940 with a tungsten core (200 g) could penetrate 60 mm of armour at 60 degrees from 400 meters, 75 mm at 60 degrees from 115 meters, and 90 mm of armour from a range of over 190 m, but less than 300 m.
The lifespan of the barrel was 600-650 shots.

Even though the gun showed satisfactory ballistic performance, satisfactory precision, good maneuverability and low visibility on the battlefield, simplicity of service and sufficient penetration, it was not adopted into service. The 37 mm ChK gun designed by E.V. Charnko and I.A. Komaritskiy was chosen instead.

The LPP-25 gun was an excellent light gun, suitable for mid-WWII. It was an excellent example of how to achieve impressive penetration with a small caliber using simple technical solutions.


Original article by Vadim Antonov.

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