The Island Line actually uses old London Underground rolling stock used on the District Line in the 1970's which displaced ex Northern Line 1930's trains.
Old it maybe but it perfectly suits the low density and short route that it operates on l think.
And very smart they are too, great people movers with a massive capacity.
We too have ordered rolling stock that has turned out to be too wide/narrow a gauge for the track it was meant to run on.