Southern Pacific Company's MC-6 class of steam locomotives is made up of two batches: the first consisting of 15 locomotives weighing 435,800 pounds built in 1912, the second consisting of 5 locomotives weighing 437,100 lb built in 1913. All of the locomotives were built by Baldwin Locomotive Works. This was the last class of 2-8-8-2 "Mallet" type steam locomotives that Southern Pacific (SP) ordered as cab forward locomotives.