English: London Underground District Line S7 S Stock train at Olympia station. The S7 Stock was introduced in 2012, making it the newest train on the London Underground network and also on any rapid transit system in the United Kingdom. It was ordered to replace the C69, C77 and D78 stock trains on the Circle, District and Hammersmith & City lines. The C Stock was withdrawn before any D stock withdrawals were made because the D stock is newer and underwent extensive refurbishment more recently and the C stock was described as being "in an increasingly poor state". Deliveries of the S7 stock are scheduled to be complete by 2016.