The SECR B1 class was a class of 4-4-0 steam tender locomotive for express passenger service on the South Eastern and Chatham Railway. These engines were originally designed by James Stirling for the South Eastern Railway (SER) in 1898 and designated B class. The SER was merged into the SECR in 1899 and, between 1910 and 1927 the B class engines were rebuilt with new boilers by Harry Wainwright to become B1 class.