25 mm ATG on MC sidecar?

[Redbeard]

I'm not sure this is the right forum, but now I'll try.

I'm working (long term) on an ATL in the early 1940s and inspired by OTL Danish Army 20mm Madsen Autocannons mounted on MC sidecars I wan't to take the concept a step further - mounting a weapon similar to the OTL French 25mm ATG on the sidecar of a heavy MC. Incl. mounting the OTL 25mm weighed a little more than 400 kg, but what would the barrel incl. recoil mechanism weigh - 100 kg? A 12-13mm MG weighed 25 kg, a 20 mm autocannon about 50 kg - would 100 kg for a 25 mm and using it from a MC sidecar be realistic?

I don't wan't automatic function, just a simple sliding breech like on the OTL French gun. I guess a muzzle brake would be handy as would be a folding down spade to lessen recoil.

BTW the 20 mm Madsens on sidecars took out 11 armoured cars and two PzI in the brief clashes on the morning of the 9th of April 1940.

The OTL French 25 mm has often been ridiculed but apparently its performance was much similar to the German 37mm - ie effective vs most tanks in service until 1942.

In an early 1940s scenario with masses of relatively light tanks being thrown into battle I could imagine 25 mm ATGs on MCs as a very effective and cheap way to counter armoured movement.

Ideas and comments are sought

 

[tomo pauk]

The fully automatic MK 103 was under 140 kg empty, while semi-automatic Solothurn S-18-1000 was at 54 kg. So the 100 kg for semi-auto 25mm ATG seems plausible, even if power/energy-wise it was a bit closer to the MK 103.
But then - why not stick the 25mm on the British recon cars (like the French did with their Panhards), that were very usable pieces of machinery for the most of time?

 

[Just Leo]

The motorcycle had to be dismounted to fire the cannon, and the headlight turned away to maybe prevent breakage. Speedo and ammeter instrument glass broke as well. The photo at left shows a bit of a wheeled cannon beside the M/C cannon. It seems transportable by two Danes.

The Belgians had a three-wheeler from FN, which offered a firing platform for twin 13.2 mm mgs for anti-aircraft use, and the French had at least three viable side-car offerings from Gnome-Rhone, Terrot and Rene Gillet.

What doesn't get mentioned a lot is that the 13 Danes who made the valiant stand all died.

 

[Driftless]

Maybe use the Motorcycle to be tractor for the towed gun? And the sidecar as caisson? that low-rider wheeled carriage would have been easier to conceal and protect.

 

[riggerrob]

Good point about adding recoil spades. Spades allow much larger calibre AT rifles to be carried. Spades also allow much quicker first shots. First shots are critical to stalling tank attacks.
Motorcycles were popular with impoverished interwar armies.

Post-war, several armies experimented with mounting 105mm recoil-less rifles on side cars.
They also experimented with mounting mortars on side cars, but I suspect that base-plates were too heavy.

In the long run, all those heavy infantry weapons were installed on ubicqutous Toyota 4x4 pickup trucks. Every warlord in a desolated Third-World nations uses "technicals" to defend his fiefdom from usurpers.

 

[Admiral Beez]

Here are some motorcycles armed with anti-tank rifles.

Russian M72 with anti-tank rifle

Hungarian motorcycle with a Solothurn ATR

http://www.wwpd.net/2016/03/bolt-action-hungarian-motorcycle-with.html

Harley-Davidson with 37mm anti-tank gun.

http://www.hdforums.com/articles/russians-bring-big-guns/

 

[Admiral Beez]

And then you've got mortar-armed motorcycles.

 

[marathag]

I will raise you with a postwar Vespa with a 75mm Recoilless

 

[Driftless]

Those machines look like something out of an Indiana Jones movie...

 

[Kevin Renner]

I will raise you with a postwar Vespa with a 75mm Recoilless

You just had to know that this would show up

 

[Somedevil]

You just had to know that this would show up

I was waiting for it.

 

[yulzari]

A detail but you need a 2WD outfit with a rear differential lock and a reverse gear for mobility or you are confined to the road much of the time. Also a goodly size of engine to pull all that weight of outfit, trailed gun, crew and kit. A jeep equivalent as the tow vehicle would be better. For the Danes they had excellent Nilfisk sidecar outfits in hand and a jeep equivalent would tempt one to go for the Madsen 37mm instead.

 

[Redbeard]

View attachment 312586
The motorcycle had to be dismounted to fire the cannon, and the headlight turned away to maybe prevent breakage. Speedo and ammeter instrument glass broke as well. The photo at left shows a bit of a wheeled cannon beside the M/C cannon. It seems transportable by two Danes.

The Belgians had a three-wheeler from FN, which offered a firing platform for twin 13.2 mm mgs for anti-aircraft use, and the French had at least three viable side-car offerings from Gnome-Rhone, Terrot and Rene Gillet.

What doesn't get mentioned a lot is that the 13 Danes who made the valiant stand all died.

AFAIK the gun could be fired from the sidecar, the photo on the left also indicate this. Anyway a fold down spade and a muzzle brake would be handy if the gun should point roughly in the same direction for the 2nd shot. Despite the 20 mm being an autocannon I guess autofire wouldn't be of much practical use in such a relatively light mounting.

Regarding the clashes at 9th of April five sections each of 2 20 mm Madsens were engaged, each section typically supporting an infantry platoon - 50 men in all. The few hours of combat in S. Jutland had 11 fallen Danes, of which 5 were from the 20 mm units. That is of course a high casualty rate among the gun crews (10-50%, depending on ammo suppliers etc. counting or not) but not unusual for those manning a weapons system attracting enemy fire and taking out 13 armoured vehicles and damaging others not a bad result. Most important is however that these very mobile 20mm units succeeded in halting very superior enemy forces. The entire 11. Motorised Regiment supported by 36 armoured cars and a company of light tanks was halted by an hour by a single infantry platoon supported by two 20mm until the ceasefire was ordered.

The events also showed the weakness of such light AT weapons however. Many of the armoured vehicles hit took several hits before being silenced. Even if penetrating the 20mm projectile only did limited damage inside the hull, but on the other hand many of the enemy vehicles took several hits.

The number of lost German vehicles appear to be confirmed but it has never been established how many men were lost on 9th of April. The claims go from 203 to a few handful.

 

[Redbeard]

A detail but you need a 2WD outfit with a rear differential lock and a reverse gear for mobility or you are confined to the road much of the time. Also a goodly size of engine to pull all that weight of outfit, trailed gun, crew and kit. A jeep equivalent as the tow vehicle would be better. For the Danes they had excellent Nilfisk sidecar outfits in hand and a jeep equivalent would tempt one to go for the Madsen 37mm instead.

I'm specifically looking for a weapon carried on and fired from the vehicle. I think the 37 mm (Bofors) will be a bit too violent to fire from a Jeep size vehicle. But going one step up, the OTL GMC 1/2 truck was mounted with a 37 mm M3 on a piedestal mount. My guess is however that you could get at least two 25 mm sidecar mounted ATGs for the price of one 1/2 ton 4x4 truck with a 37mm and the 25 mm being equal at anything but long range and much easier to conceal.

But yes the differential and reverse gear is essential for the tactics intended for these units. I BTW thought about mounting the gun reverse (Archer style) as getting out of the firing position usually is where you most want to be in a hurry.

 

[Redbeard]

And then you've got mortar-armed motorcycles.

Of course!
But OTOH here I think a small lorry or a jeep with a 1/4 ton trailer would do the same job as good as it would take 2-3 sidecar MCs to do. After all the mortar doesn't need to be in direct sight contact with the enemy and so can have a "higher profile" and has a few extra moments to mount and get away.

 

[Oldbill]

You absolutely need a VERY efficient muzzle brake. Even if you can solve the weight issue with a motorcycle/sidecar type vehicle, or a jeep type vehicle, it is still necessary to reduce the recoil of the weapon. Otherwise you'll either turn it over when firing, or ruin the suspension, or simply get killed because the vehicle rocks too much and too violently to enable you to get a fast second shot out.
Also be cognizant of the fact that your muzzle blast, dependent upon how the muzzle brake is designed, will vent the firing gasses either up/down (reducing your visibility for a second shot and showing your position to the enemy) or sideways. If they are vented sideways, you have to concern yourself with damage to your own vehicle, depending upon where the weapons muzzle is when firing. That problem can be somewhat alleviated by your prior thought regarding the gun firing to the rear, which means the muzzle SHOULD be well clear of the vehicle when firing. That also lets you "shoot and scoot", which you will need to do anyhow.

 

[Redbeard]

You absolutely need a VERY efficient muzzle brake. Even if you can solve the weight issue with a motorcycle/sidecar type vehicle, or a jeep type vehicle, it is still necessary to reduce the recoil of the weapon. Otherwise you'll either turn it over when firing, or ruin the suspension, or simply get killed because the vehicle rocks too much and too violently to enable you to get a fast second shot out.
Also be cognizant of the fact that your muzzle blast, dependent upon how the muzzle brake is designed, will vent the firing gasses either up/down (reducing your visibility for a second shot and showing your position to the enemy) or sideways. If they are vented sideways, you have to concern yourself with damage to your own vehicle, depending upon where the weapons muzzle is when firing. That problem can be somewhat alleviated by your prior thought regarding the gun firing to the rear, which means the muzzle SHOULD be well clear of the vehicle when firing. That also lets you "shoot and scoot", which you will need to do anyhow.

Certainly yes, after all the recoil energy of the 25 mm will be at least double that of the 20 mm Madsen but folding down spade(s) and low position on the sidecar are important for taking up recoil. I think the blast effect from the muzzle brake can be countered with a protective plate on the front wheel of the MC, but you have also give me an extra reason for mounting the gun "reverse" and with muzzle protruding behind the back wheels. Traverse is not important, as the gun mounting is not for general defense but rather ambushes vs. narrow points of enemy advance.

I could imagine them operating in platoons of two sections each of two guns plus infantry for close in defence and each section "leap-frogging" while falling back on more substantial defensive units and/or counterattacks.

 

[riggerrob]

Towing an AT gun is a bad idea because it severely limits your ability to turn quickly, shoot and scoot, etc.
Mounting a gun in the sidecar makes for much quicker turns though a reverse gear would be helpful.
Being able to fire rearwards (from the sidecar) is a great idea, especially if you are fighting a defensive battle like the Danes.
Maybe the solution is a dual-purpose mount that allows the gun to fire forwards (on the sidecar) during the advance and aft during retreats. Recoil spades would be hinged to the gun chassis and hang off the front or rear of the sidecar depending on today's battle plan.

 

[marathag]

Need something more like the '70s West German Faun Kraka

Rheinmetall 202 20mm for the win

3/4 ton cargo capacity, 35-40mph. Weighs 1600 pounds. For Airborne use also, the basic cargo version could fold up

It uses a BMW flat twin for power. No reason not to have something like this in the '30s.

 

[Redbeard]

Towing an AT gun is a bad idea because it severely limits your ability to turn quickly, shoot and scoot, etc.
Mounting a gun in the sidecar makes for much quicker turns though a reverse gear would be helpful.
Being able to fire rearwards (from the sidecar) is a great idea, especially if you are fighting a defensive battle like the Danes.
Maybe the solution is a dual-purpose mount that allows the gun to fire forwards (on the sidecar) during the advance and aft during retreats. Recoil spades would be hinged to the gun chassis and hang off the front or rear of the sidecar depending on today's battle plan.

I will go for the reward firing version but the dual function will not be needed as the "flying ATG" will take up firing positions, fire a few shots and then get fast on to new firing position, no matter if it is an defensive or offensive operation. But of course in offensive operations the ATGs will rather be shields/anvils than swords/hammers. A fast advancing tank unit is quite vulnerable to flank attacks and here very mobile AT units will be very handy. While the tanks advance and attack enemy positions the "flying ATGs" screen the flanks and hold any enemy flank attack until main armoured units can be turned to counter attack the counter attack.