crawlers are a given today, but their developpment back during the first world war was hilarious. The need was to be able to drive motorized vehicles off-road, through fields and other areas. The vehicles of that time were not at all suited for this kind of task. So the idea was to bring your own road with you so you don't break the wheels. This gif really shows this and I like it alot.
Russian idea before crawlers :
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The french decided it was smart to bring your own rails with you :
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Then UK withe their Mark tank and US with the Skelton showed the rest of the world how it's done.
sorry for the derail and for the images instead of gifs !