My understanding of WW1 had always been that its style of trench warfare was stable throughout the entire war. That is to say, the only defense against the new weaponry was to dig trenches, and the only way to capture trenches was to throw a few thousand men at them, at which point, you may have gained a few hundred yards. This continued until Germany ran out of resources.
What ultimately moved us past trench warfare, the story goes, was the improvement of the tank.
But a few years ago, I listened to a podcast (which may as well have been called Testosterone Drenched History, the actual name escapes me) that claimed that tactics had been updated near the end of the war; the war was becoming more mobile, ground was being transferred more quickly. It did not get into details.
I stumbled across this webpage (https://www.warhistoryonline.com/world-war-i/breaking-the-deadlock-machine-gun.html) that credits light machine gun units (with ample supplies of grenades) for breaking the stalemate.
And a piefed user supplied this somewhat cryptic (to someone who doesn´t read German Norweigan) diagram of how to take out a machine gun nest.
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[translation provided in comments: suppressive fire and toss in a grenade, repeat]
What is the true story of the tactical situation at the end of WW1?
Not really a WWI expert, but I believe that you are correct that the big factor was Germany running out of manpower.
There were also technological advances, like the rolling barrage that moved immediately in front of an advance to suppress defenders. Or the early tank. But I don’t think that these fundamentally changed the situation. They alome wouldn’t have broken a static situation.
searches
Wikipedia apparently calls it a “creeping barrage”:
https://en.wikipedia.org/wiki/Barrage_(artillery)
https://en.wikipedia.org/wiki/Tanks_in_World_War_I
I think that someone could argue that tanks were becoming a more important factor in late WWI facilitating the offensive, but they weren’t yet a major factor.
You could argue that air power, which was also emerging, would help the offensive, but that was even further out from becoming a major factor.
I think that it’s fair to say that the machine gun, barbed wire, and the trench (maybe also the land mine, though I don’t recall seeing that normally listed with the above three) favored the defensive, and that over time, other factors would come to the fore that would favor the offensive. You could say that those factors were becoming more prominent in late WWI. I don’t think that one could say that those were the dominant factors in ending the war, though.
The thing about trench warfare that makes it potent as a defensive measure isn’t the idea that no trenches can ever be captured. It’s that it slows and limits any offensive to the point that the other side cannot perform a “breakthrough”, to both penetrate enemy lines and then be able to greatly exploit that situation. https://en.wikipedia.org/wiki/Breakthrough_(military)
Germany achieved a breakthrough against French forces in WWII—they penetrated French lines and were able to, from that point, conduct a sustained offensive that led to major gains, wirh France unable to stabilize the front.
That’s the kind of thing you’d need to be able to consistently do against trench fortifications for the trenches not to be useful. If a defender can slow an advance enough that they can just dig more trenches or limit an attackers gains to a small amount and then quickly counterattack and retake them, the trenches retain their value.
I think that that tactic of having more firepower from light machine guns was tried. I don’t think that it could be said to have defeated the use of trench fortifications.
https://en.wikipedia.org/wiki/Marching_fire