Help please
 

This morning I was on a Metropolitan train between Baker Street and Aldgate.
Because there had been a person under a train at Victoria the whole of the
Circle wasn't running, nor was the District from Earls Court to Whitechapel.
As our train entered Barbican station a train passed in the opposite
direction. The destination board read "Not in Service" and there were
certainly no passengers on board but I noticed that in the last car there
were thick black cables draped along the luggage racks. What was this train
?
Cheerz,
Baz