German 15mm autocannon

[Sagittario64]

I had heard something somewhere that during the last months/year of the war, Germany was planning to reintroduce the 15mm autocannon in ther Luftwaffe. In addition to that, it has been said that production Do.335s and maybe Ta.152s were soon going to be re-equipped with 15mm cannons in place of their 20mm guns. Is this information true? What would be the advantages of a 15mm cannon over the 20mm MG 151/20? why would aircraft with high priority be armed with lesser caliber weapons?

 

[davebender]

No such thing. Germany considered weapons up to 20mm in size to be machineguns.

 

[Denniss]

That's a misinformation from some old books, probably from Green. Documents just stated MG 151 for these guns and the authors assumed it's the 15mm version. But most/all 15mm variants were rebuilt into 2cm guns thus the MG 151/20 designation (did it ever exist in official docs?) was not used anymore.
You'll see the same happen to MG FF and MG FF/M - separation was needed as long as two versions with differenr ammo were existing. The /M was dropped from about 1942 on.

 

[Siegfried]

I had heard something somewhere that during the last months/year of the war, Germany was planning to reintroduce the 15mm autocannon in ther Luftwaffe. In addition to that, it has been said that production Do.335s and maybe Ta.152s were soon going to be re-equipped with 15mm cannons in place of their 20mm guns. Is this information true? What would be the advantages of a 15mm cannon over the 20mm MG 151/20? why would aircraft with high priority be armed with lesser caliber weapons?

The originanl MG 151 was an 15mm gun. It was used on early Me 109F1 and I think F2.

The MG 151/20 was a rechambered 20mm version introduced because it was felt that 15mm round did not have enough explosive content. Some pilots loved the original MG 151 because its very high velocity made obtaining hits easier: it minimised the need for deflection shooting and fall off compensation.

Reintroducing the 15mm MG 151 on the Do 335 might make sense when one conisders that it was armed by the MK 103, a 30mm gun not to be confused with the lower velicity shorter MK 108 widely used in German aircraft. The MG 151/15 ballistics probably harmonised better with the MK 103. There may have been the intention to attack from outside of the effective range of the Browning 50 calibre.

 

[vanir]

From 1943 FW documents for Ta152B/C proposals included the C3/4/5 to be armed with 3x MK103 (docs reproduced by sqn signal iirc), two would be synchronised for ground attack, one through the hub and two defensive MG151/20 in the cowl. One prototype was built, the 190V65 but the wing root guns couldn't be synchronised, so by Oct44 the armament for the 152C3, which now encompassed all the roles of the Ta-152B/C close support variants (there was originally going to be about four subtypes with differen equipment/engines, but they cut it back to one multirole using the daimler), so at this time...

...in Die Varianten der Ta152C reproduced in Dietmar Hermann's book (dated Mar45), for actual production listings (tooling was being geared up from March), the armament for the C3 had been changed to 4x MG151 chambered for 15mm due to complementary ballistics with the MK103m motorgun. This would be because 3x MK103 was unavailable for technical reasons and it was the best second choice. It was the final armament decision for the C3.

Rechlin found their ballistics with normal AP/APT type shells surprisingly complementary up to about 600 metres varied calibre grouping with the same flight time of 1sec to 700 metres, meaning a volley from the mixed calibres is likely to strike the same target without too much trouble in a typical ground attack pass...or shooting a bomber's cockpit with pinpoint accuracy from over half a km away.

With an MK108/MG131 combination for example, you only get groupings at 150m and again at 350-450m (depending on calibration of vertical convergence set on the ground, usually 350m), once when the heavier shells passed up through the flight path of the lighter shells, again when they passed back down through them. So you could only hit with all your guns at either 150m target range, or usually 350m target range, and either side of those ranges means you hit with one gun type or another. Not both.
This is the reason for the consideration, especially for a heavy ground attack fighter, who needs at least 500m range of complementary ballistics on all his guns if he wants to hit average targets with all his guns. You walk your fire up transport columns with each target getting further away as you run out of airspace under the wings, the more lethal range you've got for each and every pass you have to make the better.

The MG151/20 and MG131 combination for fighters for example have complementary ballistics out to about 400 metres with a good grouping, and the same 1sec flight time to 500 metres. It means they don't actually group well any further out than a well set MK108 vertical convergence, but all the way out to the maximum set lethal range for convergence firing you hit with all your guns and if you walk them a bit you can still hit with all guns out to the 1sec flight time range easy enough. So you get more adaptability with the 151-2cm/13mm combination than you get with 108-3cm/13mm. You don't actually get a greater lethal range per se, just the MK108 lobs its shells in a great arc under to get to 350m true, the 2cm goes much flatter.

What you really don't want is two gun types that have different flying times as well as different "throws" as you've pretty much no chance of hitting the same target with all the guns unless you do something like they do with the MK108 in the Messer, you have two ballistic intersections between the guns tooled with a vertical convergence, you have to be pretty much exactly at that range to fire and get all of them on target. You can do that air-air but it's seriously not ideal for air-ground because you need to walk your fire around target concentrations just to hit something in the first place, and the plane might not want to do exactly what you want in this 2D environment where it will in a 3D environment because the target is flying relative to you, not moving relative to the gound.

The MG151 15mm ammunition was stockpiled already. The rechambering of the 151 for 2cm was a little sudden and unexpected from my impressions although a real expert like Tony Williams would know the history of the weapon more than me. The BoB hadn't been lost when production was tooled and the emphasis was on a dual purpose motorgun with tungsten option, in 1941 the emphasis changed and included pilot protest, so that now they wanted a single purpose air-air gun with m-geschoss option instead.
So the 15mm has tungsten rounds available but no m-geschoss. The 2cm version has no tungsten but has m-geschoss option.

So it is a matter of both complementary ballistics and readily available ammunition, because you arm planes for the role you want them to do. And the 15mm was meant for dual purpose, that is a ground attack (light-AP) function. It fires flat, true for a long way and goes though an engine block. The 2cm has a bigger punch but sacrifices some of these qualities. ROF is pretty much identical between the calibres.

 

[Sagittario64]

Thanks. ballistics harmony was the reason i read that i couldnt remember when i made this thread

 

[Denniss]

The problem with using the 15mm version was, almost all of them were either converted to 2cm weapons or spread out to many units for secondary installations. I don't think the tools to made the 15mm barrerls were still in existance.
I have seen a weight table for an Do 335 A-6 which specifically calls the gun MG 151/20.

 

[davebender]

1945 aircraft so a gyro stabilized gunsight would be planned. Combat ranges increase from 200 meters to 800 meters. High velocity weapons become a lot more important. The MG151/15 might need to do until the MG213 revolver cannon enters mass production.

 

[Tante Ju]

The problem with using the 15mm version was, almost all of them were either converted to 2cm weapons or spread out to many units for secondary installations. I don't think the tools to made the 15mm barrerls were still in existance.
I have seen a weight table for an Do 335 A-6 which specifically calls the gun MG 151/20.

Heer had Hanomag with 151/15 Flakdrilling.

 

[Denniss]

Heer had Hanomag with 151/15 Flakdrilling.

As I said, spread all over the different branches of the Wehrmacht and you'll have to collect them all if you want to re-use them in a new fighter production. That's why they used the 2cm gun in most Do 335.

 

[Erich]

the 15mm Flakdrilling was used primarily against soft ground targets very effective on the Ost front. in the halftrack version could not be traversed quickly enough to follow low moving craft

 

[CharlesBronson]

The advantage could be a flatter trajectory of the 15mmm projectile compared withe 20mm ammunition because the higher muzzle velocity, however the rate of fire isnt great 700 rpm.

By the way the 15mm is a heavy machinegun not an autocannon.

http://www.ww2aircraft.net/forum/we...ftwaffe-cannons-machineguns-topic-6368-3.html

 

[davebender]

I think 20mm mine shells were a lot more effective against soft targets. Otherwise the Heer would have replaced 20mm flakvierling with 15mm flakdrilling by 1942.

m. SPW
The Sd.Kfz 251/21 was manufactured between August 1944 and March 1945. Like so many other late war German weapons I suspect it was hastily produced using whatever bits and pieces were at hand. Somebody found a stash of MG151/15 machineguns so that's what they armed it with.

 

[Erich]

my point is that the drilling was an effective soft skin killer in 1945 with many W-SS and Heer units operating them amongst their armor on the Ost front.

 

[Sagittario64]

I know i said autocannon. thats because i thought all weapons 15.0mm and greater were considered cannons.

 

[Sagittario64]

And if 20mm cannons were becoming less effective with their explosive power against better armoured allied aircraft, and 30mm cannons were too heavy and slow, and the allied .50cals were showing to rip german aircraft apart, wouldnt a 15mm MG 151 with flatter trajectory and more penetration power(at the cost of explosive power) look more attractive?

 

[tomo pauk]

Perhaps you might state the kind/category of Allied aircraft 20mm cannons were becoming less effective, and then compare weight , say, number of engines for German fighters and those Allied planes?

 

[Tante Ju]

And if 20mm cannons were becoming less effective with their explosive power against better armoured allied aircraft, and 30mm cannons were too heavy and slow, and the allied .50cals were showing to rip german aircraft apart, wouldnt a 15mm MG 151 with flatter trajectory and more penetration power(at the cost of explosive power) look more attractive?

Except aircraft armor didn't upgrade much or all during war.. this is most annoying myth I see. That aircraft became better armored. 99% of fighter bombers for example had no armor at all, and even very slow 20 mm cannon had massive punch penetration if using AP ammo..

No aircraft was safe against 20 mm ammo. Not even Shturmowik.

 

[Shortround6]

And if 20mm cannons were becoming less effective with their explosive power against better armoured allied aircraft, and 30mm cannons were too heavy and slow, and the allied .50cals were showing to rip german aircraft apart, wouldnt a 15mm MG 151 with flatter trajectory and more penetration power(at the cost of explosive power) look more attractive?

A little thought exposes this myth. steel weighs 40lbs per square ft per inch, a 1 foot (30.5cm) wide by 1 foot (30.5cm) high plate by 1 in (2.54cm) think weighs 40lbs (18.18kg). NO aircraft could carry enough armor to cover ALL the vulnerable spots. Pilot armor helped the pilot to survive, it didn't do much for the airplane as a whole. Pilots, who were saved by their armor either bailed out of their shredded aircraft or brought back damaged aircraft needing repairs (if not written off) to make them combat worthy.

The American .50's reputation is somewhat over blown. It did shoot down German, Japanese and Italian aircraft in numbers. It did not penetrate more armor than most 20mm guns.

 

[Frantish]

Wouldn't a 15mm AP round been effective in ground attacking?