Union Pacific 4012

Union Pacific 4012
"Big Boy" 4012 on static display at Steamtown National Historic Site
Type and origin Power type Steam Builder American Locomotive Company Serial number 69583 Build date November 1941
Specifications Gauge 4 ft 8 1⁄2 in (1,435 mm) Fuel type Coal
Career Operators Union Pacific Railroad Class 4884-1 Numbers 4012 First run 1941 Last run 1962 Disposition Static display at Steamtown National Historic Site

Union Pacific 4012 is one of the world's largest steam locomotives and is one of eight preserved Union Pacific Big Boy locomotives. Built by American Locomotive Company in November 1941, Big Boy 4012 was retired in 1962 and can be viewed at Steamtown National Historic Site in Scranton, Pennsylvania.

Union Pacific 4012, nicknamed "Big Boy", is a 4-8-8-4 type locomotive built by American Locomotive Company in November 1941. It is among the world's largest steam locomotives. One of 25 built, No. 4012 is one of eight of its type to survive the advent of the diesel era. Referred to as an "articulated" locomotive, because it has more than one set of drivers, Big Boy weighs 1,250,000 pounds (570,000 kg). This locomotive worked for 21 years hauling freight between Cheyenne, Wyoming, and Ogden, Utah, logging over 1,000,000 miles (1,600,000 km) before its retirement in 1962.

4012 was originally on display at Steamtown, U.S.A in Bellows Falls, Vermont, until 1984 when Steamtown USA moved to Scranton, Pennsylvania. Since the Steamtown turntable and roundhouse are too small to accommodate the size and weight of 4012, it has remained out-of-doors since its arrival at Scranton.

The Steamtown Special History Study recommended that this locomotive remain at Steamtown because it is the only articulated locomotive in the Steamtown USA collection and recommended that due to its good condition, 4012 could be restored to working order. However, the study also recommended that 4012 remain on static display, because it is doubtful that the "track, switches, culverts, trestles, bridges, wyes, turntables, and other facilities that would have to carry her [could] bear her great weight".