This book covers the design of RT 1, the 2RT2s and the 3RT3s. When RT 1 entered service in 1939, no-one would have imagined that the type would be in London passenger service until 1979, almost double the life of its immediate predecessor, the STL. As with the RM, the type's early years in service were not without a number of mechanical problems and initial production was cut short by the outbreak of war. By the time production recommenced in 1947 numerous design changes had been made, all of which are detailed here.