They were built between 1923 and 1924, 75 by Baldwin and by Lima Locomotive Works .

The first batch of 25 were built by Lima, and numbered 6175-6199.

The second batch was built by Baldwin, and numbered 6200-6224.

[1] They were nicknamed "big sixes" because until renumbering in 1954 their road numbers all began with 6.

[1] Locomotives numbered 6009 and 6030 were scrapped in 1925, and their boilers used to build new Class T 4-8-2 Mountain Type locomotives numbered 5500 & 5501.