wrote in message
...

Why SDO? The East London line had 5-car OP stock in 1971. Or is SDO needed
just for the only station that didn't exist then, Canada Water?

Like most LU stock, historic or current, carriages are often significantly
shorter than mainline stuff. The 5 cars of 15.5m (approx) O/P stock would
still be less than 4 x 20m 378s.

But yes, Canada Water is also one of those places difficult to extend...

Paul S