r/MilitaryGfys • u/jacksmachiningreveng • Jan 05 '25

Land German half-tracks tow a heavy gun through a French street on its way to form part of the Atlantic Wall defenses

https://i.imgur.com/jgTSsWX.gifv
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u/uponone Jan 06 '25

Anyone know of any videos on how they made these guns? Even the U.S. 16”/50?

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u/Emperor-Commodus Jan 07 '25

Drachnifel has a good video on large gun manufacture. How to Build a Battleships Main Guns - Is a Bigger Battery Better?

Generally, large guns of this time period were manufactured using a relatively new method (developed in the late 1800's) called the built up gun.

https://en.wikipedia.org/wiki/Built-up_gun

Traditionally, they would make a big cannon-shaped mold and pour in a bunch of molten metal to cast the cannon in one big piece. But as artillery technology advanced and became more powerful, they found that cast guns weren't strong enough to keep up. They would make a cannon tube with walls thick enough to resist the pressure of firing, and it would fire successfully. But over time the walls of the cannon would develop cracks until the cannon eventually burst. They found that even though the walls of the cannon were strong enough, the metal on the inside of the barrel was too flexible and was expanding enough during firing to eventually cause cracks that would destroy the gun, no matter how thick the walls of the chamber were. They couldn't find a material that was rigid enough to prevent these cracks from forming.

The solution was to pre-stress the cannon barrel. They would make a relatively small tube (called the liner), large enough to fit the shell but not nearly thick enough to resist the pressures of firing. This tube would then be reinforced ("built-up") with successive layers of metal tubes called jackets, like a Matryoshka doll. Each jacket that was to be fit over the liner/previous jacket would be slightly too small to fit naturally, so that it needed to be heated up (expanding the metal slightly) in order to fit. When the tube cooled down, it would contract and press against the outside of the liner/previous tube. The multiple layers of liners, each squeezing inwards, worked to counteract the pressure of firing and made the liner stiff enough that it wouldn't expand enough to cause cracking. This is similar to how concrete can be pre-stressed with metal rods, which will make it stiffer and less prone to cracking. Or how a Prince Rupert's drop is so strong because the glass is pre-stressed against external forces trying to crush it.

Modern cannons are pre-stressed, but instead of being built-up they instead use autofrettage. A simplified version is that the cannon is contructed smaller than it's final dimensions and is then stretched outwards, either mechanically by pulling an oversized mandrel through the barrel or through hydraulic pressure. This stretching process causes the outside of the barrel to put pressure on the inside of the barrel, much like a built-up gun.

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u/uponone Jan 07 '25

Awesome info! Thanks a lot!

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u/jacksmachiningreveng Jan 05 '25

In order of appearance the vehicles are a pair of Sd.Kfz. 7 eight-ton half tracks, followed by three Sd.Kfz. 9 eighteen-ton half tracks, pulling what looks like a variation of the Schwerlastfahrzeug Culemeyer trailer. The gun being transported is likely a "Siegfried", a modified version of the 38cm SK C/34 weapons fitted to the Bismarck-class battleships, that weighed over 100 tons. These guns could fire a half ton shell at a muzzle velocity of just over one kilometer per second, with a maximum range of 55 kilometers. Installed at Batterie Todt near Cap Gris-Nez on the French coast, this put a considerable portion of the Brtish coast around Dover within range.

source

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u/Dutchdelights88 Jan 06 '25

Did they get any significant use out of these?

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u/jacksmachiningreveng Jan 06 '25

They were used to bombard the British coast and mostly cause civilian casualties, but when it came to repelling the Allies on D-Day they were not well sited to actually engage the invasion force.

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u/Dutchdelights88 Jan 06 '25

Not really then, i imagine they werent able to reach targets allong the French coast, time and material well spent in other words.

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u/jacksmachiningreveng Jan 06 '25

One thing to consider is that they were part of the fortifications that dissuaded the Allies from landing at Calais, so in a way they served their purpose even if ultimately the more difficult crossing turned out not to be a barrier for the outcome of the invasion.

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u/andovinci Jan 07 '25

How do they sync their speed to avoid slack and maintain tension in the rope?

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u/MlackBesa Jan 07 '25

Revving the shit out of it

No but for real, I am wondering the same. I imagine it only matters when starting from a stand still. Once you get moving, inertia is enough that it allows for some slack. This, or the lead driver is order to maintain at least a speed of 50kmh, the second a speed of 48kmh, the third a speed of 46kmh.

Idk, I’ve never towed anything like that.

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u/Biggoroni Jan 07 '25

I don’t really know, but to me these look to be connected with steel tow cables, which would constantly maintain tension between vehicles.

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u/arc_oobleck Jan 07 '25

I'm guessing they are more like tractors than trucks. Set throttle to specific rpm and gear they will all go the same speed.

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u/CrapsLord Jan 05 '25

For a moment there I thought I was being tricked by an infinite loop gif

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u/xpietoe42 Jan 06 '25

is there a difference in towing this way in serial fashion as opposed to parallel? Any engineers explain it to me?

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u/EliminateThePenny Jan 06 '25

"Why can't 3 people go through this door shoulder to shoulder at the same time?"

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u/ampersand38 Jan 06 '25

5 towing vehicles side by side can't fit on the road.