Saturday, 18 November 2017

Devourer of Tungsten

In late summer of 1942, the Red Army captured a German weapon that piqued the interest of the Red Army Main Artillery Directorate. This was the new German tapered bore 7.5 cm Pak 41. Several shells were captured along with the gun, which allowed trials to be performed and several characteristics to be determined. What was this gun, and what were the results of its trials in the USSR?

History

After the first encounters of the Germans with new Soviet T-34 and KV tanks in June of 1941, it was clear that the 3.7 cm Pak was ineffective against them. Anti-tank defense had to be performed with AA and field artillery firing over open sights, but these guns were ill-suited for this task: they were too large, insufficiently mobile, and offered little protection for their crews. Germany accelerated work on anti-tank guns.

Pak 41 on trials at the Gorohovets proving grounds, fall of 1942.

One of the directions for improving the power of anti-tank artillery was the creation of a tapered bore, using a principle invented by engineer Hermann Gerlich. The  2.8 cm schwere Panzerbüchse 41 (2,8 cm s.Pz.B. 41) was another such gun. The principle allowed the creation of an effective anti-tank gun with a high muzzle velocity, which meant better penetration, but also spawned a whole heap of problems. The most grievous ones were a low barrel life and the consumption of rare and expensive tungsten, which was used to make shells.

By mid-1941, tungsten was in deficit in Germany, as supplies came from far outside the Third Reich. Special blockade runner ships had to deliver it from overseas in small amounts. Mass production of a weapon that fired this metal was not the best idea, but that was the quickest possible method that industry could propose.

By January of 1942, two 75/55 mm caliber (75 mm at the breech, 55 mm at the muzzle) guns were proposed: a combined Rheinmetall and Krupp proposal called Schwere 7.5 cm Pak 44 and Krupp's own 7.5 cm Pak 41.

Blueprints of the 7.5 cm Pak 41 barrel.

Trials showed that the lifespan of a Schwere 7.5 cm Pak 44 barrel was only 250 rounds. The 7.5 cm Pak 41's barrel was no better, but the design allowed for replacement of the section of the barrel that wore down the most in the field. As a result, the 7.5 cm Pak 41 had an advantage.

Due to the inability to supply the guns properly, only 150 units were ordered. Production began in March of 1942. A separate note was made that the production of these weapons decreased the number of subcaliber ammunition with a tungsten carbide core available for other anti-tank guns.

The gun cost no more than the traditional Pak 40 (15,000 Reichsmarks vs 12,000), which appeared slightly later. It took 2800 man-hours to build one gun. 

Production was spread out in the following way: March: 48, April: 25, May: 77. Military acceptance was performed with some delay. 4 guns were accepted in April, and the remaining 146 in May.

Use in battle

Out of 150 guns, 141 were immediately shipped to the Eastern Front and distributed among anti-tank squadrons of infantry and motorized divisions. Excited reviews began to return soon after.

Gun from the 36th anti-tank squadron, 36th Infantry Division in position. Bagranovichi region, spring of 1944.

In August of 1942, the Wehrmacht lost three guns, and one of them was retrieved by the Red Army intact, along with a small amount of armour piercing shells. In total, 17 Pak 41 guns were lost before the end of 1942.

"Shell hunger" forced the Germans to seek out a replacement for tungsten, but a new type of shells for the Pak 41 with a steel core performed significantly worse. In addition, the more traditional Pak 40 proved itself worthy, and large amounts were shipped to the front.

By April of 1943, the Wehrmacht had 78 Pak 41 guns left. Some of the losses were noncombat, as guns were stripped for parts. On July 25th, 1943, a note appeared in the journal of the Wehrmacht Supreme Command:

"Due to a lack of spare parts and difficulty with ammunition, Army Group Center passed 65 7.5 cm Pak 41 guns to the Supreme Command of the West, where they were repaired, reorganized, and subsequently used for coastal defense."

A low profile is an important feature of any anti-tank gun, and the Pak 41 met this requirement.

However, the Atlantic Wall soon ceased to have any use for these guns due to a lack of armour piercing shells. However, they were not written off or scrapped. The guns remained in service until 1944 and fought against the Western Allies.

The number of Pak 41 guns available steadily declined. Only 56 remained by February 1st, 1944, 44 by April 1st, 35 by September 1st, and only 11 guns survived until March 1st of 1945.

Trials in the USSR

As mentioned above, one of the guns ended up captured by the Red Army, and the GAU instructed that trials should be performed on October 6th. The trials were performed to compose a technical description of the weapon, determine penetration, and ballistic qualities of the system. Special attention was to be paid to the recoil mechanisms, semiautomatic mechanisms, and breech. 

Pak 41 anti-tank gun during trials at the Gorohovets proving grounds.

The gun arrived along with six shells at the Gorohovets proving grounds on October 22nd, 1942. The shell type is written down as "Pzgr.40", but that is a mistake, as the conical barrel of a Pak 41 would have been torn off by a regular shell. It is impossible to determine today what kind of shell was used.

Stability trials (jumping, recoil, surging) were performed during firing to determine ballistic properties. Three shells were spent to perform this. Since the sight was lost, the gun was aimed by looking down the barrel.

Only three shells remained for penetration trials. It was planned to fire at a 120 mm thick plate from 200 meters. The first shot would have been made against the plate at an angle of 60 degrees. If penetration was not achieved, it would have been fired at an angle of 90 degrees. If the armour was penetrated on the first try, the target for the second shot would be 140-150 mm of armour at 60 degrees.

7.5 cm Pak 41 ammunition cutaway.

Trials did not go according to plan. The proving grounds had no 120 mm thick armour plates, so two 1.2x1.2 m plates of different hardnesses were used, one 100 mm thick and one 45 mm thick. These plates were positioned at a 60 degree angle. The 100 mm plate was already fired upon, and it was deformed. It was not possible to put the plates right up against each other, so a 30 mm space remained between them. The gun fired from 200 meters, aiming through the barrel.

The first shot missed. The second was fired from 100 meters. Alas, it was also a failure: the shell hit the wooden frame that held the plates. The third shot, fired from 75 mm, hit the mark. The ballistic cap deformed, the core penetrated the 45 mm plate, shattering into tiny pieces, and the sabot was stuck between the plates.

The shell after hitting the armoured plates.

Even one hit was enough to conclude that the Pak 41 could penetrate 120 mm of armour at a 60 degree angle. Calculations showed that it would be able to penetrate 195 mm at 500 meters and 170 mm at 1000 meters. Due to a lack of shells at the Gorohovets proving grounds, the calculations of the Artillery Committee could not be confirmed.

The trials ended there. Based on the muzzle velocity of 1190 m/s, one can guess that the Pzgr. 41 St. shell was used: a steel core, and not a tungsten one.

Description of the 7.5 cm Pak 41

The 75/55 mm caliber anti-tank gun was designed to combat tanks and armoured vehicles, and could also fire to suppress strongholds and destroy enemy personnel.

It was transported by a mechanized transport, and was equipped with a suspension mechanism, which activated automatically when the trails were joined, and a pneumatic brake, which could be activated by the transport driver. The wheels were metallic, with solid rubber rims. The split trail carriage allowed it to fire over a 60 degree arc.

Gun shown from the crew's point of view.

The main parts of the gun were the barrel and breech, cradle with recoil mechanisms and a ball mount, the elevation and traverse mechanisms, a shield, and the sight.

The Pak 41's design did not include an upper and lower mount, a standard feature of all gun designs of the time. The shield performed the function of the lower mount. It was built from two 7 mm thick armoured plates, reinforced with ribs in between.

A cradle with a ball mount, the suspension, and aiming mechanism were attached to the shield. The shield protected the crew from small arms fire from all ranges and shell fragments, to some degree. The barrel was installed in a ball mount in the middle of the shield, a feature typical of fortress guns rather than anti-tank ones. 

The breech was a vertical semiautomatic sliding type. The optical periscopic sight only allowed for direct fire. The sight was located in the upper part of the cradle. The sight design allowed the gunner to account for barrel wear.

7.5 cm Pak 41 in travel position.

The monobloc barrel consisted of the tube, adaptor, barrel collar, muzzle brake, and breech. The breech was connected to the tube with a connector. The adaptor was screwed into the tube, for which it had slots for a wrench. The opening between the tube and the connector was covered by the collar, which was attached with a screw. The tube had 28 constant twist rifling grooves. The caliber of the tube was 75 mm along its length, and the length of the tube was 2965 mm.

The adaptor had a more complicated design. Its channel combined the cylindrical and conical parts, without any rifling. Most of the wear happened to this part of the barrel, and the design allowed for rapid replacement in the field. The adaptor was 950 mm long. The caliber was 75 mm at one end and 55 mm at the other. The length of the conical part was 450 mm, the length of the cylindrical part was 500 mm. The muzzle brake was of the slotted type and screwed into the end of the adaptor. The gun allowed for vertical aiming from -10 to +18 degrees.

Some historians incorrectly interpreted the blueprints and accompanying text, as a result of which they decided that the adaptor was split into two parts.


Ammunition for the Pak 41 and a tube container for transport.

Four types of ammunition were developed for the 7.5 cm Pak 41
  • Pzgr. 41 H.K.: armour piercing tracer ammunition with a tungsten carbide core. Mass 2.58 kg, muzzle velocity 1260 m/s.
  • Pzgr. 41 St.: armour piercing tracer ammunition with a steel core. Mass 3.00 kg, muzzle velocity 1170 m/s.
  • Pzgr. 41 W.: armour piercing tracer ammunition. Mass 2.48 kg, muzzle velocity 1230 m/s.
  • Spgr. 41: high explosive tracer grenade. Mass 2.61 kg, muzzle velocity 900 m/s.
The 7.5 cm Panzerjägerkanone (Pak) 41 was a unique weapon with excellent characteristics that was a threat to both contemporary tanks and post-war vehicles. Only a small number and a lack of tungsten prevented it from showing its full strength. Meanwhile, the appearance of this weapon prompted the USSR to begin working on its own analogues, especially since new types of German tanks were already known, and the performance of the Pak 41 was impressive.

7 comments:

  1. Very interesting, do you have more details on the angles definition? Can you confirm if it is with respect to a vertical axis?

    ReplyDelete
    Replies
    1. From horizontal, I don't think that it would be able to pierce a plate at 90 degrees from vertical :P

      Delete
    2. D'oh I was thinking about the tank armour setups. thanks!

      Delete
  2. Aside from the problems of getting the stuff in the first place, one reason tungsten was at such a premium was that it was needed for various machine tools. Being able to manufacture more things had something of a priority over furnishing some of those things with inherently expendable special-purpose ammunition...

    ReplyDelete
  3. Apparently Japan made a copy of this gun in 1943 and mounted it on a couple vehicles, though it was also cancelled for a lack of tungsten: https://www.reddit.com/r/Warthunder/comments/5ybezw/type_ge_75mm_anti_tank_gun_natochito/

    ReplyDelete
  4. the image of the shell shows the deformed remains of a Pzgr41W (7.5cm/5.5cm CPBC).
    The -W would deform but not break up, kind of a low efficiency APSH projectile with identic terminal ballistics to the Pzgr 41Hk. The -W is only effective against medium thickness, high hardness armor. Unlike full calibre AP, the penetration was less affected by high obliquity impact.
    It had a much lower penetration coefficient compared to either full calibre AP or APCR (De Marre K=2400-2500). Due to the designed for deformation action, an HE filler was omitted.

    ReplyDelete