English: London Underground S7 Stock leaving West Ham station in July 2013. Having been introduced in 2012, the S7 Stock is the newest train on the London Underground network. The S7 stock, along with the S8 stock (which was introduced in 2010), is one of two subtypes of the London Underground S Stock. Other than differences in the number of coaches (the S7 stock has 7 coaches while the S8 stock has 8), the interior layouts are different - The S8 stock contains a mixture of longitudinal and transverse seating, while the S7 stock contains transverse seating only. Both trains are air-conditioned (being the first trains on the network to feature air conditioning) and have gangways that allow passengers to safely move between carriages while the train is moving, unlike older trains on the network. The S8 stock is used on the Metropolitan line and was ordered to replace the A stock on that line - the A stock reached 50 years of service in 2011 and was therefore the first stock to be replaced, the final A stock withdrawal happening in 2012. The S7 stock is used on the Circle, District and Hammersmith and City lines and was ordered to replace the C stock and D stock on those lines. The older C stock was replaced first since the D stock was extensively refurbished in the mid 2000s and the C stock was described as being "in an increasingly poor state". The final C stock withdrawal happened in 2014 and the D stock is to be replaced by the end of 2016.