Saturday, 20 August 2016

Schwere Panzerbüchse 41

In 1942, the Allies captured an interesting anti-tank weapon designed for the German army and actively used on all fronts of WWII since 1914. Its distinguishing feature from other anti-tank rifles and cannons was its conical barrel, the caliber of which was larger at the breech than at the muzzle.

Officially, the gun was called 2,8 cm schwere Panzerbüchse 41 (2,8 cm s.Pz.B. 41). German nomenclature placed it into the small arms category, but both the Red Army GAU and the military ministries of Great Britain and the United States classified it as artillery. The difference in classification comes from the fact that this weapon has all the characteristics of a cannon: carriage (upper and lower), shield, mount with a recoil brake, but the aiming was done by hand, by moving the gunner's body and moving the barrel up and down.


Captured 2,8 cm s.Pz.B. 41 on trials in the USSR.

Various samples were captured by the Allies at different times, and were tested independently on various proving grounds. In the USSR, the GAU was in charge of trials. The guns were disassembled and carefully studied, instructions on assembly and disassembly were written, blueprints drawn up. Interestingly enough, Soviet, American, and British documents are almost entirely identical. The s.Pz.B. 41 was studied and recorded in 1942. The British included a description of the gun in a reference of enemy weapons in December of 1942.

History

In the early 20th century, 1903-1907, German professor Karl Puff worked on improving the muzzle velocity of sells. He proposed variable caliber barrels that were slightly conical. In order for the shell to not get stuck in the barrel, it had a special directing rim that engaged the rifling tightly. As the barrel narrowed, the rim was compressed into a special indentation in the shell. This kind of projectile used the energy from burning gunpowder more effectively that traditional firearms, but the lifespan of the barrel was shorter and making it was complicated.

Gerlich's conical barrels and bullets for them (US patent 1944883).

After the end of WWI, Hermann Gerlich continued Puff's experiments in creating an infantry weapon with a high muzzle velocity. The biggest difference from earlier designs was that the bullets had two rims instead of one. This increased the stability of the bullet in flight, preserving its high speed. Several carbines with Gerlich's conical barrels were tried and tested in the late 20s and early 30s. These weapons set records for muzzle velocity that still haven't been beaten, but the drawbacks of the design (high cost and low lifespan) were still unsolved.

In 1934, Gerlich died in strange circumstances, and all technical documentation and results of his experiments ended up in the hands of Mauser engineers in Obendorf. In 1939, they created a light universal infantry weapon that used Gerlich's principle, with a 28/20 mm conical barrel, named Gerät 231 or MK.8202. Initially, the system was supposed to be fully automatic, but that feature was later dropped.

Captured 2,8 cm s.Pz.B. 41 with a first type carriage on trials in the USSR.

An experimental batch was produced in the summer of 1940, which was sent out for field trials. After correcting some defects that the trials revealed, the gun was accepted into service with the Wehrmacht with under the index 2,8 cm schwere Panzerbüchse 41.

When the Germans faced T-34 and KV-1 tanks in their war with the USSR, it turned out that the s.Pz.B. 41 could penetrate them in favourable circumstances, although the probability of that was low. By 1943, it was obvious that the weapon does not meet requirements for anti-tank guns. However, it remained in use until the end of the war as a measure against lightly armoured vehicles and trucks, as well as the suppression of machinegun nests and cannons.

s.Pz.B. 41 on a wheeled carriage. The carriage design and shield configuration are visible.

The 2,8 cm schwere Panzerbüchse 41 was produced at the Mauser factory in Obendorf. The cost of one unit was 4500 Reichsmarks. The productions schedule was as follows:
  • 1940: 90 units
  • 1941: 339 units
  • 1942: 1029 units
  • 1943: 1324 units
In 1942, a tank variant of the 2,8 cm schwere Panzerbüchse 41 was designed to replace the 2 cm KwK guns, named 2,8 cm Kampfwagenkanone (2,8 cm KwK 42). 24 units were built, but by 1942 it was no longer reasonable to arm tanks with this gun, and the idea was rejected.

Technical Characteristics

The weapon was designed to combat tanks and armoured cars, as well as destroy armoured and unarmoured emplacements. Thanks to the simplicity of aiming and loading, relatively low weight, and small size, the gun was mobile and maneuverable.


Diagram of the barrel and breech.  (Enemy weapons. Part III. German light anti-aircraft and anti-tank guns. The War Office. December 1942)

The weapon used a quarter-automatic mechanism, automatically closing the breech, which allowed for a rate of fire of up to 10 RPM (by German data) or 12-15 RPM by GAU's data (20 unaimed shots). Effort on the breech lever was about 5 kg. The loading operation could be done in 0.8-1 seconds.

The quickly removable barrel consisted of a monobloc tube with a removable muzzle brake and connected to the breech with a screw connection and then affixed with a clip.

Cutaway of the s.Pz.B. 41.

The breech connected to the cradle which housed the recoil mechanism. The horizontal sliding breech was equipped with a safety and hangfire protection. The breech opened manually and closed automatically once a round was chambered.

The first guns were equipped with an open sight attached to the counterweight, but later an optical sight was used. The gun could only fire directly with either type of sight.

To deliver the s.Pz.B. 41 to a position inaccessible by wheels, it could be disassembled (without instruments) into parts that could be carried by the crew. Regardless of the carriage type, it had five parts: the shield (two pieces), barrel and muzzle brake, carriage with breech and counterweight, upper and lower mounts, and the limber/trailer.

The crew consisted of five men: commander, gunner, loader, and two ammunition carriers. Firing the gun was very loud, so the use of earmuffs was mandatory.

Transporting the s.Pz.B. 41 in parts through the mountains.

When the gun was transported in parts, the commander carried the barrel, the gunner and loader carried the upper and lower parts of the mount, and the ammunition carriers took the carriage and gun shield. The limber was not carried. Ammunition was carried in cases of 12. The case was identical to the 3.7 cm Pak one, only the label on the cover was different.

The weapon had the following characteristics:
  • Muzzle velocity: 1400 m/s
  • Effective range: up to 500 meters
  • Barrel length: 1.7 meters
  • Number of rifling grooves: 12
  • Caliber: conical, 28/20 mm
  • Mass of the shell: 121 g AP, 91 g HE (according to GAU data, 93 g)
  • Mass of the barrel and muzzle brake: 37 kg
  • Mass of the shields (both): 22 kg
  • Lifespan of the barrel: 500 shots

2,8 cm Sprgr.-Patr. 41 and 2,8 cm Pzgr.Patr. 41 shells, illustration from "Artillery ammunition of the former German army. Reference. USSR Armed Forces GAU. Ministry of Defense of the USSR publisher, 1946"

Available ammunition types included:
  • 2,8 cm Panzergranatpatrone 41 (2,8 cm Pzgr.Patr. 41) – armour piercing
  • 2,8 cm Panzergranatpatrone 41 (Üb) (2,8 cm Pzgr.Ptr. 41 (Üb)) – practice
  • 2,8 cm Sprenggranatpatrone 41 (2,8 cm Sprgr.-Patr. 41) – high explosive
  • 2,8 cm Platzpatrone (2,8 cm Pl. Patr) – blank
  • 2,8 cm Exerzierpatrone (2,8 cm Ex. Patr.) – dummy
The penetration of the 2.8 cm Pzgr.Patr. 41 was as follows:


German data
Soviet data
British data
American data
100 m, 90 deg
94 mm
Up to 75 mm
84 mm

100 m, 60 deg
69 mm
40-50 mm
69 mm

500 m, 90 deg
66 mm
Less than 40 mm
Less than 65 mm

500 m, 60 deg
52 mm
25 mm
Less than 53 mm
Less than 53 mm

Soviet penetration data was extrapolated based on the Jacob de Marre formula (K=2400).

Gun Shield

The gun shield consisted of two independent shields: the main shield and the gunner's shield. Each was composed of two plates, 4.5 mm and 5.5 mm thick. The plates were joined by bulletproof bolts, the same as on the Pak 38 and Pak 40. The space between the two plates was 46 mm. The edges were made wavy so the gun was easier to conceal.

Two s.Pz.B. 41 guns with different shields, the first type on the left and the second type on the right (Canadian War Museum in Ottawa and the French Tank Museum in Saumur, respectively).

The main shield was positioned in the front and protected the crew. It was attached to the upper mount with shock-absorbing pins. The gunner's shield was attached to the breech and protected his head during shooting. Both shields are removable. During transport, the gunner's shield was attached to the main shield. The main gun shield of the first 90 s.Pz.B. 41s produced differed slightly from the rest of the production run (the shape of the gun opening is different). 

Cradle

The box-type cradle was permanently attached to the upper mount. The upper part of the cradle directed the recoil mechanisms. The rod that cocked the hammer during recoil was also attached to the cradle, as was the counterweight. The counterweight also contained the trigger mechanism and sight. The counterweight was hollow and had instruments inside.

Cradle and counterweight.

The rear of the counterweight had two handles used for aiming the weapon and the trigger mechanisms. The handles were very comfortable and the size and form of the handles followed the shape of the hand. The gunner could firmly hold the gun and could fire at any time without letting go of the handles.

Moving the gun in the vertical plane took 3-5 kg of effort. Turning the gun took only 1-2 kg. This type of aiming method allowed the gunner to traverse a 60-70 degree arc in one second, whereas a flywheel based aiming mechanism would take about 15-20 seconds. An experienced gunner could aim at a new target within 2-3 seconds, whereas the 3.7 cm Pak or Soviet 45 mm gun would take 6-12 seconds (8-9 seconds on average).

Carriage

Two types of carriages were designed for the weapon (the cradles and barrel remained the same). The upper and lower mounts were different.

Lafette mit Fahrgestell: a carriage with wheels. Consisted of the cradle with recoil mechanisms, upper mobile mount with shock absorbers, lower immobile mount with the trails, shield, sight, and wheels with suspension.

Wheels and suspension.

The box type trails were the same, with the exception of the parts that joined them together in travel position. A bar with a ball joint limited how far the trails could be spread. Spades were welded to the rear of the trails.

The trails were attached to the lower mount, which acted as a foundation for the upper mount and was attached to the suspension.

Trails, upper, and lower mounts.

The upper mount could rotate independently of the lower mount, and held up the oscillating part of the gun (cradle, breech, and barrel), the oscillation dampener, and the main shield.

The gun could fire either from the wheeled mount or from the ground, which drastically decreased its height. In both cases, the trails were deployed. The wheels were the same as on the Infanteriekerren 8 cart.

The gunner's position depended on the gun's position. If the gun was on wheels, the gunner was kneeling, otherwise it was only possible to fire while prone.

Firing with wheels removed.

The wheel section was equipped with a leaf spring and rubber foam-core tires, and was designed to move the s.Pz.B. 41 over short distances. The gun was often hitched to the Infanteriekarren 8 cart, which was used as ammunition storage. Two men could easily transport the gun on wheels over a distance of 300-500 meters or more, walking and partially running. At the GAU proving grounds, soldiers could transport the s.Pz.B. 41 500 meters over loose sand in 5.5 minutes. It took 5-7 seconds to prepare the gun to fire after being transported on wheels.

When transported over large distances, the Sd.Ah.32/2 (Sonderanhänger für schwere Panzerbüchse 41) trailer was used, equipped with special ramps to wheel the gun in.

s.Pz.B. 41 gun and Infanteriekarren 8 cart. The gun was brought into position in this manner.

Only 90 units of these carriages were made. Surprisingly enough, the guns captured and tested by the Soviets and the British both used this carriage.

Technical data of the s.Pz.B. 41 on a carriage of the first type:
  • Total length: 2580 mm
  • Mass with wheels: 223.2 kg
  • Mass without wheels: 162.22 kg
  • Horizontal range: 60 degrees
  • Vertical range: +25 to -15 degrees
  • Lower and upper mount weight: 57 kg

Mountain soldiers with s.Pz.B. 41 guns in transport position on Sd.Ah.32/2 trailers.

After 90 units were made, field trials showed that the design does not meet the army's requirements and is too heavy. Starting with the 91st gun, the s.Pz.B. 41 was made with a different carriage.

Leichter Feldlafette (leFl): a lightened carriage with a different upper and lower mounts, as well as the wheel base. A hollow pipe design and use of lighter alloys allowed a significant reduction in weight. The different design meant that the elevation and traverse angles changes.

Lightened carriage with ammunition containers.

Instead of a wheels base with leaf springs, the lighter carriage had smaller removable wheels. The mass of each wheel and its axle was only 5 kg. These small wheels were enough to move the gun into positions.

The spreadable trails were also discarded. Instead, one removable pipe trail was used, reinforced with a T-bar and ending with a wide spade. Two oval pipes bent into a complex shape were used as side rests. The lower mount was simplified. The upper mount was now made from a cast swivel. The function of the upper and lower mounts did not change.

s.Pz.B. 41 on a lightened mount. The wheels are collapsed, and you can see the rear trail of the carriage.

It was possible to fire with the wheels on or off. In the latter case, the stability of the system was improved and its height decreased. It was not necessary to remove the wheels completely to fire from the ground, only to loosen a bolt (without any instruments) and turn the wheel on its axis. The overall length of the gun remained the same, the mass with wheels and without was 147 kg and 137 kg respectively.

A lightened trailer to transport the new mount, the Sonderanhänger für schwere Panzerbüchse 41 auf leichter Feldlafette (Sd. Ah. 32/3), which only weighed 85 kg. Wheels from the Infanteriekarren 8 cart were used.

Lightened Sd. Ah. 32/3 trailer for transporting the s.Pz.B. 41 with a lightened carriage (Saumur tank museum).

The s.Pz.B. 41 with a new carriage and trailer weighed a little more with the trailer than the old type of carriage did without it.

After being accepted into service, the s.Pz.B. 41 was sent to motorized units, tank divisions, SS units, independent anti-tank squadrons, airborne units, and mountain units.

s.Pz.B. 41 gun on an Sd.Kfz. 250 halftrack, Grossdeutschland division («Schützenpanzer» by Bruse Culver & Uwe Feist. Ryton Publications).

Installation of this gun on lightly armoured vehicles using various improvised mounts was very common. Many photographs exist of these guns being used on various modifications of Sd.Kfz. 250, Sd.Kfz. 251, and Sd.Kfz. 221.

The last time these guns were used during WWII was during the fighting in Berlin in 1945.


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