Southern Pacific class AC-11

Southern Pacific Railroad's AC-11 class of cab forward steam locomotives was the seventh class of 4-8-8-2 locomotives ordered by Southern Pacific (SP) from Baldwin Locomotive Works; SP was so pleased with the AC-10 class built a year earlier that the railroad began placing orders for AC-11s while the AC-10s were still being built and delivered. They were built between November 1942 and April 1943, closely resembling the AC-10s.

Southern Pacific class AC-11
SP 4274 leading an excursion train out of Reno, Nevada, on December 1, 1957.
Type and origin Power type Steam Builder Baldwin Locomotive Works Serial number 64677 – 64706 Build date November 1942 – April 1943
Specifications Configuration: ​  • Whyte 4-8-8-2 Gauge 4 ft 8+1⁄2 in (1,435 mm) standard gauge Driver dia. 63 in (1,600 mm) Adhesive weight 531,700 lb (241,200 kg; 241.2 t) Loco weight 657,900 lb (298,400 kg; 298.4 t) Boiler pressure 250 psi (1.7 MPa) Feedwater heater 6SA Worthington Cylinder size 24 in × 32 in (610 mm × 813 mm) (bore × stroke)
Performance figures Tractive effort 124,300 lbf (553 kN)
Career Operators Southern Pacific Railroad Class AC-11 Numbers 4245 – 4274 First run November 24, 1942 Retired 1954 – 1958 Disposition all scrapped

The first AC-11, number 4245, entered service on November 24, 1942, and the last, 4274, on May 9, 1943. SP used these locomotives for between 12 and 15 years, with the last retirements from this class occurring on September 24, 1958. Shortly after their retirement, the AC-11s were scrapped, with the last, number 4274, on April, 1959.