Thursday, April 16, 2015

How effective were AT rifles against the Pamzer III?

The case of the Pz IIIs. 

All the Pz IIIs with 37mm guns had only 30mm of front armor. The first 50L42 armed model, the G, had the same. The first to uparmor, to 30mm plus 30mm additional bolted on the front hull only, was the H model. The turret was still 30mm, at around 15 degrees slope (the G and H mantlets were somewhat thicker, 37mm). Both Gs and Hs were made between the fall of France and the invasion of Russia, with twice as many of the G model produced as Hs. 

By the time of the invasion, production of the J model with the 50L60 gun had begun, but most of the existing fleet were the older models. This model had 50mm front plates factory built, and a 50mm mantlet, but the rest of the turret front was still 30mm. The J series had the largest production run of any of the letters, as production began to ramp in 1942. They were produced from before the invasion until a year after it. 

The last year of Pz III production, as tanks rather than StuG that is, were the L-N versions, from mid 1942 to mid 1943. These had 57mm turret fronts, 50mm base front armor elsewhere, and in addition 20mm additional plates bolted on to the upper front hull and gun mantlet. Through this whole uparmoring process, the turret sides and rear, and the hull sides, remained 30mm only. 

The final production vehicle of the Pz III series was the StuG. The early StuG had the 75L24 gun, same as in the Pz IV, and had 50mm of front armor - like the Pz III J model - with the same 30mm sides naturally, since they used the same chassis as the Pz III tanks. By late war standards, not many of these were produced. 

The first upgunned StuGs, the F models, had 75L43 guns, and originally the same armor as before. The same expedient of bolting on extra armor plate was used, to thicken the front from 50mm to 50mm+30mm (going from 2 inches up to 3 inches thick, basically). The gun mantlet was not uparmored and remained 50mm. Late model F series, toward the end of 1942, had the 75L48 and the extra bolted armor. 

The last production model of the StuG III, the G model, was the type produced from 1943 to the end of the war, and in the late war by far the most common type. Everything you'd see in CMBO is this model. It had 80mm front armor factory built, and the 75L48 gun. The sides are still the same 30mm as the original Pz III had all around - plus skirts.

The side armour of the StuG and Panzer IV were just as weak in 1944 and 1945 as they were in 1943 when Schürzen was introduced. The AT-rifle also remained effective against lightly armoured vehicles like the SdKfz 251, effectively an infantry fighting vehicle operating against Soviet infantry.

According to Steven Zaloga, approximately 1/2 million AT-rifles were produced during the war with 37.000 still being turned out in 1944 and the Soviet Rifle division nominally had 111 such weapons in its inventory in June 1945 (down from 279 in 1942).

Of course, Schürzen were originally tested against direct HE fire as well, and that threat hadn't disappeared either.

KPB - AT Machine gun (1944) Penetration 32 MM at 90 degrees at 500 meters. ROF 70/minute. 
PTRD - (1941) AT rifle Penetration 37mm at 300 meters. 

PTRS (1941) AT rifle. ROF 15/minute, Penetration 35mm at 90 degrees at 300 meters, 25mm at 500 meters. Germans used captured ones as PzB 783(r). Could penetrate 50mm vertical armor at 100 meters. (PzIV had 50mm vertical front armour) 

So at very close distances these could be quite deadly to tanks like PzIII and PzIV.

The official design requirement was that at a range of 500m it should penetrate 20mm of case-hardened armour at 70 degrees.

The BS.41 bullet used in the ATRs had a tungsten-carbide core and was a very good performer. I have figures of penetration (at 60 degrees in all cases) of 30mm/100m, 27.5mm/300m and 25mm/500m.

The penetration data is for 60° from vertical, or 60° from horizontal (30° from vertical).

Penetration loss with range looks very small for such a light weight round.
60 degrees from horizontal.

The 14.5 fires a heavy bullet which probably doesn't slow down that much up to 500m, but I agree that the fall-off in penetration looks low. The figures are from a secondary source on anti-tank rifles. If anyone has a primary source I would be interested.

The 14.5mm API had a small-arms style of bullet, i.e. with a complete streamlined jacket (in steel, coated with gilding metal or (later) zinc) and with the AP core filling most of the bullet. There was a gap between the blunt-nose core and the jacket tip and this was filled with incendiary material. This design was copied by the US for their .50 cal M8 API round used in late-WW2 and Korea aircraft guns.

In the BS.41 the core was tungsten carbide and the bullet short and flat-based. In the BS-32 (which may have followed it into production) the core was steel and the bullet longer and boat-tailed.

My source is Labbett & Brown's Technical Ammunition Guide 2/4 on Soviet 12.7mm and 14.5mm ammo - very good, lots of sectioned drawings!

I suspect that the main advantage of the plates was that penetrating them might cause the bullet to tumble and hit the armour side-on, greatly reducing effectiveness.

The Luftwaffe found out that just penetrating 3mm alloy aircraft skin before hitting armour would reduce effectiveness of AP bullets by up to 30%.

Thoma - or Drahtgeflechtschürzen were adopted in September '44, starting with Fgst.Nr. 92301, so any unit receiving Pz IV Ausf. J after this date should theoretically have them, although the usual first in/last out process of assembling tanks may throw a spanner or two in the works here.

The small-caliber AT-rifles used early in the war (7.92mm etc.) was not very effective. The Soviet 14.5mm PTRD and PTRS were different beasts all together. They were effective against lightly armoured vehicles like the German SPWs (SdKfz 250/251) and sufficiently powerful to cause the Germans to adopt "Schürzen" to protect the lower hull of the Panzer III, IV and Sturmgeschütz.
The entire Panther project was nearly cancelled because the lower hull armour was considered to weak to withstand (future?) Soviet AT-rifles. Had it not been possible to put Schürzen on the Panther, it would have been replaced by the Panther II! (See Jentz: "Panther..." p. 35 and 53)

The German problem with the Soviet AT-rifles was not that they were very effective against German tanks - the problem was that on a good day with a lucky gunner, one of these dirt-cheap and primitive weapons could knock out a 100.000 Reichmark tank. That was not acceptable and the Germans put a lot of design effort into conquering this problem.

Of course, the AT-rifles would also be effective against vision slots, periscopes and other weak spots and openings in the tanks armour.
One would think that expanded metal grating would be not much harder to produce than plate, while providing the weight and material savings of wire mesh. Or was such a product not part of the German industrial "toolkit" in the 1940's?

Sound dumb does it not? Well, it is

It was not the wire-mesh shields that posed problems, it was the brackets attaching them to the hull. None had been developed at this time (February 1943) and designing them would delay the issue of Schürzen. (Jentz/Spielberger: "Begleitwagen.." p. 198)

When Schürzen were first tested in 1943, both wire-mesh and plate were used. Results showed that both were equally effective in stopping AT-rifle rounds and HE. It was decided to use plates because wire-mesh was more complicated to produce and the facilities for producing plates were already there (see Jentz & Spielberger: “Begleitwagen” and Spielberger: “Sturmgescütze...”)

Schurzen Side Skirts
The previously mentioned Schuzen side-skirts became a topic of discussion during the Fuhrer's conference on 6 and 7 February 1943. Hitler was quite in agreement with mounting skirts on the Panzer III, IV and Sturmgeschutz to provide protection against Russian anti-tank rifles. Test firings on Schurzen protective skirts (wire and steel plates) were reported on February 20, 1943. Firing tests utilizing the Russian 14.5mm anti-tank rifle at a distance of 100m (90 degrees) showed no tears or penetration of the 30mm side armor, when protected either by plates or wire mesh. When testing was conducted with the 75mm high explosive shell (Charge 2) from a field gun, there was no damage to the sides of the hull armor when protected by the wire or plates. Wire mesh and plates had indeed been penetrated and even torn away, but, they still remained usable.
The decision to utilize the plates as opposed to the wire mesh (although both had proven effective and the mesh was lighter) was based on the fact that the wire mesh required the design of a new mount, which would have required additional time to be developed.
Additionally, the procurement of wire mesh for the side skirts was difficult. The skirts were not tested against shaped charges, nor were they intended as protection against shaped charge (HEAT) shells.
On March 6 1943, Hitler indicated that he was satisfied with the favorable results of the firing tests against the Schurzen side skirts. In addition to outfitting all newly produced Sturmgeschutz, Panzer IV and Panthers with side skirts, all armored vehicles of these types currently deployed and those undergoing maintenance, were to be backfitted with them. The schedule for fitting Schurzen was to be expedited.