 They were built in three batches of 1, 9 and 10; their first running number was chosen at random from the numbers left vacant by locomotives that had been transferred to the duplicate list.This fate was almost immediately suffered by the 317 class – after only one or two months in service.All passed to the London, Midland and Scottish Railway in 1923, who initially allocated them the numbers 6400–6419 in the passenger tank sequence.