Why does the German Army like 20mm auto cannons so much?

[davebender]

More specifically, why does the German Army like the 20mm x 138mmB / 20mm x 139mm cartridge so well? They have used it in a wide variety of weapons from the 1930s right up to the present day. Not that I have anything against this cartridge but why do they prefer it over readily available auto cannon cartridges that are more powerful?

Panzer II ausf C. Mass produced 1937 to 1940.
Historically armed with KwK30 or KwK38 auto cannon chambered for the 20mm x 138mmB cartridge. Not a bad light tank but why wasn't it armed with the much more powerful 3cm Mk101 / Mk103 auto cannon?
Armor Penetration.
49mm @100 meters. 20mm x 138mmB cartridge. Same for KwK30 and KwK38.
75mm @ 300 meters. 30mm x 184mmB cartridge. Mk101 cannon.
70mm @ 300 meters. 30mm x 184mmB cartridge. Mk103 cannon.

RH202 auto cannon. 20mm x 139mm cartridge.
Main gun for Marder IFV, Luchs recon vehicle, various flak mounts etc.

The RH202 is ok but what happened to the 30mm MG213C revolver cannon that was operating in prototype during 1945? Britain copied this weapon as the ADEN cannon and it has been very successful for dozens of nations. The MG213C has a more powerful round, a higher rate of fire and yet the weapon weighs only 87kg. What's not to like? Germany created a fantastic 30mm weapon yet the Heer chose to stick with a slightly improved version of their WWII era 20mm cartridge right into the 1980s.

 

[Shortround6]

1.Because the MK 101 didn't exist when the 20mm x 138B cartridge was adopted.
2. The 30mm guns were bigger and heavier, the MK101 was almost three times heavier than the 20mm guns.
3. Size and weight of the ammo. The MK II tank carried about 180 rounds of 20mm ammo in 18 ten round magazines. It used a one man turret ( many descriptions are wrong). while tanks are not really weight sensitive they are very volume sensitive. MK 101 could be feed with 6 round boxes but given the size of the ammo the magazines are going to be bigger and heavier and harder to change, gun breech takes up more room in the turret. Using a belt feed means you cannot change the type of ammo from AP to HE or from normal AP to an APCR or APDS round.

RH202 auto cannon. 20mm x 139mm cartridge.

In standard loading's the older round had about 47,000 joules of muzzle energy, the new round has 72,600 joules for the HE round and 84,000 joules for the AP. A bit more than a "slight" improvement. The 20mm round for the MG213C had a muzzle energy of 61,700 joules. The rate of fire for RH202 is 800-1000rpm vs the 1200-1400rpm of the WW II gun. Without a 350-700mph slipstream of cooling air for the gun barrel high rates of fire from a single barrel can be a real problem. The New gun incorporates a dual feed. Two belts go into the feed mechanism and the gunner can select which belt (type of ammo) in 1-2 seconds. This is harder to do with a revolver cannon.

 

[davebender]

1935.
3cm MG101 developed by Rheinmetall-Borsig. It was evolved from an existing 20mm AT weapon.
…..Note. MG101 was original weapon designation and used through 1940.

1937 to 1940.
1,113 Panzer II ausf C produced.
…..Assumption. MG101 cannon not yet production ready.
…..Point of Departure. The Panzer II turret will be designed for the 3cm MG101 cannon. The 2cm cannon will be employed as an interim weapon just as the 3.7cm cannon was employed as an interim weapon on the Panzer III. Consequently the Panzer II turret (including ammo storage) is sized to fit the larger weapon. Heer 8 wheel armored cars (Sd.Kfz 232, 233 and 234) will also use this turret.

July 1939.
MG101 cannon tested in Me-110B aircraft. 10 round magazine.
…..Assumption. MG101 cannon production ready NLT this date. Might have been made production ready sooner but that would be speculation.
Historical Luftwaffe procurement of MG101 cannon was tiny. The Heer will fund procurement of 200 weapons per month from fall 1939 onward. Hence this cannon will become a Heer program.

September 1939.
German invasion of Poland. 16mm armor on early war Panzer IIs proved vulnerable to Polish AT rifles. Consequently frontal protection of existing vehicles was improved by adding 20mm armor plates. New production Panzer II had 30mm frontal armor built in.
…..In this scenario existing Panzer II are rearmed with the 3cm MG101 cannon while at depot for the armor upgrade.

 

[Shortround6]

And this gets you what when the T-34s and KVs show up?

If you can stuff a MG101 in the turret you could probably stuff in the regular 37mm tank cannon.
You need a bigger turret ring anyway.

 

[davebender]

32 ton T34s and Sherman tanks don't become a serious problem until 1942. Until then most armored vehicles weighed less then 20 tons and were armed with a 37mm or 45mm main gun. Threats the dirt cheap Panzer II can handle if armed with something more powerful then the historical 20mm cannon.

The 10 ton Panzer II could probably be armed with a 3.7cm/45 main gun. Personally I think the 3cm MG101 auto cannon is a superior overall weapon. Multiple hits in close proximity allow you to chew through armor. You cannot do that with a single shot weapon.

 

[tomo pauk]

If we really want a tank for Heer, wielding the 3cm autocannon, perhaps Pz-38(t) is better choice?

 

[Shortround6]

The armor penetration figures given are for tungsten cored shot. Using normal AP shot penetration falls to 32mm or under. Germans had a shortage of tungsten and while they did use in the aircraft guns for tank busting (because using the normal shot would have been near useless) equipping hundreds of tanks with guns that are going to out of ammo in short while doesn't make a lot of sense.

 

[davebender]

Why?

- The Panzer II ausf C and Pz-38(t) are both 10 ton tanks.
- Both have rough riding leaf spring suspension.
- 25mm frontal armor on Pz-38(t) ausf A through F is inferior to 30mm frontal armor on 1940 later Panzer II.
- Early model Pz-38(t) use inferior riveted construction rather then welding.
- I haven't seen a production cost for the Pz-38(t). But I doubt it costs less then the dirt cheap Panzer II.

Don't get me wrong, I think the Pz-38(t) was ok for such a small tank. But IMO the similiar size Panzer II would be as good or better if it had a more powerful main gun.

 

[Shortround6]

Actual armor penetration figures for the MK 101 were 25mm/300m/90^ for the 500gram APHE. This was improved to 32mm/300m/90^ with the later higher velocity 455gram projectile. Both penetration ratings fell of with both angle of impact and range. The Tungsten cored stuff (355 grams) could do 75mm/300m/90 degrees (or better depending on armor)but it's performance fell of worse with both range and angle of impact. Impacting at 60^ caused it's penetration to fall to between 42-52mm.

As an example of the fall off in performance of the tungsten cored rounds in these small sizes the German and Czech 37mm guns had better performance with standard ammo at ranges over 500yds than they did with the Tungsten cored rounds.

The Pz-38(t) had a least a two man turret and the Germans may have crammed in a third man (loader). in combat this beats the heck out of the one man band act going on in the MK II turret. If you want the MK II to be an effective combat tank it needs to be all new from the top of the tracks up. Not only a new turret but a new upper hull to hold the new turret.

Dirt cheap is not always an advantage. The Czech tank was noted for it's reliability and cross country performance.

 

[davebender]

I doubt any tank with leaf spring suspension had good cross country performance as the ride would be rough.

Germany developed torsion bar suspension for the Panzer II during 1941 but that's too late to matter for such a small tank. Under different production circumstances it might have made a good full track APC chassis.

 

[Shortround6]

The engine in the 38(t) was about 25% bigger in displacement which means more torque. Nobody was doing more than 8-12mph cross country no matter what suspension without throwing the crews around. Many tanks only had shock absorbers on first and last road wheels if they had them at all. Cross country ability is also hill climbing, ground loading, and a bunch of subtle things not usually found on quick fact sheets. British Churchills could climb hills better than Shermans despite much lower top speed and the later Centurian was also better in very rough terrain than the M-46-48 series. They may have moved at a walking pace but that is better than not moving at all.

A several variants on the 38(t) chassis went to 15-16 tons. The MK II didn't go beyond 11.5 tons without a suspension change. Granted they might have put heavier springs in the heavy 38(t)s but they didn't add road wheels or change the entire suspension.

 

[parsifal]

Germans used their light tanks, principally the PzII and Pz 38 as Assault guns later in the war. Basically rip out the turret and replace with a gun 75mm or 76.2mm. SPGs with this armament was a better re-use of a scarce tank chassis that refitting or redesigning it with an already inadequate gun.

Pz IIs were only ever intended as stopgaps. Sounds to me this upgrading scheme would be a major investment in redesign for not much return. Germans were pinning their hopes on the Pz III/IV combination, with the PzIII equipped with a 37mm gun when designed.

Re-equipping the PzII with a redesigned experimental gun in a redesigned turret in a redesigned turret ring takses the PzII from nbeing dirt cheap, into the realm of the problematic.....

 

[davebender]

IMO a 50% weight increase is not a variant. It's an entirely new armored vehicle chassis even if it's derived from an older vehicle. Anyway this isn't meant to be about armored vehicles per se.

Getting back to the main topic...
Early model Marder IFVs weighed 28.5 tons. By 1989 the upgraded Marder A3 weighed 35 metric tons. Similiar in size to a T-34 or Sherman tank. So why is it still armed with a 20mm cannon? The Heer could have chosen something larger such as the M242 chain gun (i.e. Bradly IFV) or 30mm Rarden cannon (i.e. Warrior IFV) and still had room for an infantry fire team.

 

[Shortround6]

what is the point? None of those guns will take out a tank except from the rear. APC were/are turning into light medium tanks with an infantry component. Bigger guns mean less ammo. If you want to blow up enemy armored vehicles just put a missile or two on the vehicle. At the cost of a modern IFV the cost a missile is a cheap kill and you still have the 20mm for soft vehicles and general support. Maybe the Germans like the idea of just enough gun to do the job without giving the Marder crews delusions of grandeur about tank hunting.

 

[parsifal]

You would have to say, however that Marders along with the US Bradleys are an over-investment for limited protection. Maybe thats what Dave is on about, though I doubt that upgrading to a 30mm cannon will make any difference to the survivability of the type.

Israeli doctrine does not support frontline use of APCs as MICVs. They have found that in their normal operating environments, such vehicles are far too vulnerable for any such role. I have my doubts about the whole MICV concept.....riding into battle in a AT rich environment in inadequately armed and protected vehicle is a sure way to get a whole bunch of Infantryman killed IMO. The Marder /Bradley options add to the conundrum by making such vehicles expensive additions to the inventory....reduces the number that can be deployed because such vehicles are too expensive.

There were problems in the Iraq deplyment of the bradleys, though I forget what those issues actually were

 

[kettbo]

Having served some 8-9 years on Bradleys in every crew and platoon position during my 20 years of service as a Cavalry Scout, I can share some insights.
20mm (German) and 25mm (Bradley) do terrible things to light armored vehicles, soft targets, troop type targets
Yes, the Bradley is complex, costly, but it is capable, very capable. Great mobility and a healthy cruising range. The best defense is a good offense!!! Pretty tough cookie though not a tank by any means. Great sensors, great fire control (the last 12 years or there about with the Laser Range Finder), outstanding weapons.

NEVER EVER consider a single piece of equipment on a modern battlefield as stand-alone.
You'll not find too many people these days blindly charging into a stiff defense. In a suspected AT-intense envoronment, before the attack, Air Scouts, UAVs, Multi-Sensor assets, or 19D Cav Scouts infiltrating prior to or ahead of the attack locate said AT weapons and cause their destruction via TacAir, Gunships, or indirect fires. Or simply avoid the area of heaviest defense. There are too many good weapons available to make the enemy 'good enemy.' If you have 120mm mortar fire "Immediate Suppression" or "Final Protective Fire" you would be amazed at the destructive fire by this BN asset., "No waiting" so to speak compared to 155mm fires from supporting artillery. We would often team 3 M-3 CFV with two tanks, hunter-killer. I'm sure you can find a Combined Arms Live Fire Exercise video on YouTube, lots of destruction in a very short period.
Here is one such vid

View: https://www.youtube.com/watch?v=2cRp-fJNl-4
something for everybody here. the vid does a good job of showing all the pieces, the last bit shows everything going on at once when all the cards are played.

Sure, from time to time something gets missed and there will be AT vs BFV action. The platoon vehicles are scanning through thermals or optical sights, covering one another. Suspected areas are neutralized with Smoke/WP or HE, or direct fire from the BFVs 70/230 25mm rounds in the ready boxes. The M-2 Infantry fighting vehicle carried less ammo and missiles due to carrying the Infantry squad. The M-3 CFVs had considerable space and stowed a considerable arsenal. The 25mm ammo boxes had switches for the rounds in each to adjust the reticle reference. Often the CFV would be AP-heavy with Sabot in the 230 box and 70 HE in the small box. This in order to defeat enemy recon vehicles, PCs, etc.

vs Tank, really not where you want to be, especially in the offense. Operating as sections with Bounding Overwatch, one section covers the other as they move. Covering section has the TOW launchers up, scanning, preferably from some sort of protective terrain or hull down. On the defense, certainly under cover with only the thermal sights exposed... Leave enemy tanks for your tanks or the gunships.

 

[parsifal]

Hi kettbo

I know that the bradleys are an exceptionally capable piece of kit, as are the marder2s. however, i guess I am looking at the issue from the quatermasters POV, and comparing that to some of the "cheaper" options kicking around at the moment.

Bradleys cost something in the order of $7m (Au), per copy. A Marder2 if it were being produced today would cost about $9-11m (AU). If you compare that to say our ASLAV-25, which is similar to your LAV-25, but with enhanced fording and amphib capability, the cost is about $2.5m per copy. ASLAV/LAV -25s carry the same armament....dont know the sensors, but I expect are similar, are AWD rather than tracked, and only very lighly armoured (designed to withstand small arms). Obviously they are a more limited vehicle than the bradleys, but for every one Bradley you can have nearly three ASLAVs. But its worse than that. If your Bradleys are even remotely similar to the old M-113s (shows my age, but thats equipment I am a little more familiar with), the tracked APCs wont have near the longevity between refits. M-113s needed a complete replacement of tracks every 5000 kms or so. ive heard Bradleys suffered similar serviceability issues in Iraq. LAVs I am told just kept going and going.

So, taking into account the servicieability issues, which is the better deal...having one Bradley, or 4 or 5 LAVs.
Australian Army in Afghanistan and iraq, have gone even lower in the firepower stakes, so as to enhance reliability, and lower cost. our bushmaster vehicles are armed with nothing bigger than a 50 cal, and are only 4wd as opposed to 8WD in the LAVs. They are armoured, but even less so than the LAV. Yet they cost only a fraction, at $0.5m per copy, and with very high rates of serviceability. We have found these typeds of vehicles in places like Afghanistan a far better option than even the ASLAV.

Unless the army has unlimited resources, it makes sense to opt for reliability at the expense of hi tech sophistication. Tracked APCs, tend to be just that, and APCs with high levels of firepower tend to be a waste. I happen to think the best compromise is the LAV option, but perhaps I am wrong....

 

[davebender]

Nor do they need to as we are now discussing an IFV. Primary purpose of the main gun should be to provide infantry with effective fire support. That eliminates the WWII requirement for specialized infantry support vehicles such as the StuGIII, Su-76, Sherman 105 and various British infantry tanks. Perhaps the German Rh202 20mm cannon works well for that purpose. But to me it seems a bit small for defeating dug in infantry. On the flip side, Rh202 cannon rate of fire is outstanding compared to larger IFV weapons. It must be murderous against soft skinned vehicles and infantry caught in the open.

Flugabwehrkanone 20 mm Zwilling
Rheinmetall 20 mm Twin Anti-Aircraft Cannon - Wikipedia, the free encyclopedia

If mated with an effective fire control system a pair of Rh202 cannon ought to turn any aircraft into Swiss cheese. Lightweight and compact too. Looks like a worthy sccessor to the WWII era flakvierling. But it has a short effective range just as the WWII era weapon did. Perhaps that's not an issue as long range flak is now accomplished using surface to air missiles.

 

[kettbo]

Just a word on AAA
If the flyboys see tracers zipping past, concentration on the flying, bombing, switchology tends to suffer.
Nobody wants to get hit by a Golden BB so until neutralized, AA fire will be avoided.



The threat of a major war in Western Europe (la raison d'être for the Bradley and Marder) diminishing, only low intensity conflict on the horizon, the US Army switched to Stryker production. The Stryker allows more units to be built, easier deployability, less maintainence heavy for sure, and less fuel used.
The trade off is less protection and less firepower per vehicle. Many versions of the Stryker; one for recon, Infantry, AT Missile, tank-like AGS
I have no personal experience with Strykers in deep mud such as we encountered regularly at Grafenwohr or Hohenfels or a Korean winter. Fair or mild weather, roads, advantage to the wheeled vehicles. Cross country, mud, bad weather, tracked is where it is at.

5000 km is a very long time for a tracked vehicle if you think about it. I have seen quite a few tires flattened/shreaded and wheels blown off by stuff that whould not phase a Bradley or Marder. Lots of hi-tech stuff out there allows more to be done with less boots on the ground.

25mm DU rounds have been known to penetrate older WP tanks
10-15 rounds into the side/rear of a T-72, could get interesting. Not a good way to make a living however, too risky. But tanks have optics and other vulnerable things that can be damaged if you cannot get killing hits.

.50 cal has impressive penetration. In a power mount with optics, quite lethal on point targets at usable distances. But I must return to what I said earlier about multi systems. Pin the enemy to fix his position, then call in 120mm mortar, artillery, or air to eliminate him. With 20mm, you get longer range and some explosive in the projectile, better penetration. 25mm, more of the same.

Which system works better? For Iraq and Afghanistan, the lighter vehicles do well. A major confrontation in Europe over real estate could have those with lighter vehicles at a major disadvantage. Regrets, "Joe" does not get to choose where he goes to war or what he is equipped with.

 

[davebender]

Marder and Bradley IFVs have been deployed to these conflicts. Which main gun has proven better in modern combat?

25mm M242 chain gun (i.e. Bradley IFV). 200 rounds per minute.
20mm Rh202 cannon (i.e. Marder IFV). 1,000 rounds per minute.

I suspect the larger 25mm rounds would be superior for fighting enemy BMPs. But what works best vs enemy infantry? That Rh202 cannon can put an impressive quantity of 20mm mine shells on target.