The articulated wheel-base steam locomotive represents the final phase of steam locomotive development in size and power. The cab-in-front feature was widely used by the Southern Pacific Railroad beginning in 1909 to alleviate smoke and heat problems for locomotive personnel en route through tunnels and snow sheds. This locomotive, built by the Baldwin Locomotive Works, operated between 1944 and 1956 before being displaced by a diesel-electric locomotive.
California State Railroad Museum
111 I Street
Example of the final phase of US steam locomotive development in size and power
Courtesy Wikipedia/Neil916 (CC BY-SA 3.0)