The train that's half a mile long

At half a mile long, it's Britain's longest ever train - and can be found travelling through the night with a small army of workers onboard.

But apart from sounding impressive - the train in this clip has a really important job.

It's used to clear away old 'ballast', the rocks and stone that support the train tracks, and replace it with new stuff.

It's travelling overnight between Norwich and London at the moment to make sure the train line is in good shape. You can see it in action above.

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