for the east west and north south lines, six types of rolling stock are used. the oldest is the c151, built in 1986-89 by a collaboration between kawasaki heavy industries and three sub-companies, kinki sharyo, nippon sharyo and tokyu car corp. 66 trainsets are in operation, which were upgraded between 2006 and 2008. 19 more c651s were purchased in 1994 from siemens ag, followed by 21 more c751b sets, built in 1999-2000 by kawasaki heavy industries and nippon sharyo. two companies, kawasaki heavy industries and csr sifang, have collaborated to build 3 types of rolling stock. the fourth rolling stock in operation is the c151a. they were built between 2010 and 2014, and started operations in 2011. the next rolling stock that started operations is the c151b, which began operations on 16 april 2017. the newest rolling stock, being built between 2017 and 2018, is the c151c, and it began operations on 30 september 2018.