According to this article, the former D78 stock trains that once ran on the District Line of the London Underground are now being operated by GWR on the line between West Ealing and Greenford. While the ex-D Stock trains on the Isle of Wight are the third rail-powered Class 484 EMUs, the GWR trains are battery-electric Class 230s, which recharge through certain sections of the track.

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Talk about a homecoming for the D-Stock.

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Also, a bit of a reversal. Back in the day, the original GWR ran locomotives on what would become the London Underground. Now, we have (former) London Underground stock running on a GWR line.

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Very true.

Jago Hazzard just did a video on it.