The first California cab-ahead design (also known as a cab-forward) was built in 1901 by William J. Thomas, master mechanic of the North Pacific Coast Railroad. Its unique design was possibly influenced by an Italian cab-ahead which had received much publicity in the trade press. The configuration provided the best visibility for locomotive engineers on sharp curves. Southern Pacific officials also recognized the value of the cab-forward as a design that would save engineers from being asphyxiated by smokestack fumes in SP's numerous long mountain tunnels and snowsheds. The first cab-forwards were delivered to SP by Baldwin in February 1910. Engine 4294 was part of SP's AC-12 class (Articulated Consolidation type, twelfth series group) locomotives, the last new steam locomotives acquired by the company.
The cab-forward design worked well on these large articulated locomotives. An articulated is equipped with two independent sets of driving wheels, able to follow the rails flexibly. SP No. 4294 is often incorrectly called a Mallet. Named for its French designer, Anatole Mallet, the Mallet is not only articulated, but it is also compounded, meaning the steam is used more than once. The steam goes first to high pressure cylinders, then to low pressure cylinders. Early cab-aheads on the SP were Mallets. SP 4294 is articulated, but not compounded, and thus is not a true Mallet.
In total, Baldwin built 256 cab-forward locomotives for SP, the only American railroad to make extensive use of this design. Wheel arrangements for these oil-burning behemoths were 2-6-6-2 (changed to 4-6-6-2 after a serious derailment), 2-8-8-2, and 4-8-8-2. Although they were identified mainly with the Sierra Nevada, these locomotives also saw service on the Tehachapi Mountains, the Shasta Division, the Modoc route and other parts of the SP system.
SP 4294 was in service from March 19, 1944 to March 5, 1956, hauling both freight and passenger trains in California and Oregon. The 4294 occasionally pulled the famous Overland Limited (Train Nos. 27 and 28) over the arduous Donner Pass route between Sacramento and Sparks, Nevada.
In September 1958 the now dieselized SP wrote-off its twenty-nine remaining cab-forwards. The Pacific Coast Chapter of the Railway & Locomotive Historical Society organized a campaign to save No. 4294 from the scrap heap. SP responded by putting the engine "on hold" while the rest of the cab-forwards were scrapped.
SP 4294 was placed on outdoor display in front of SP's Sacramento station and dedicated to the City of Sacramento on October 19, 1958 in a celebration that also featured the
C. P. Huntington. Both locomotives were moved in 1967 to make way for an Interstate 5 approach ramp. They temporarily appeared at the Sacramento station in May 1969 for the Gold Spike Centennial Celebrations.
For eleven years No. 4294 was stored in SP's Sacramento yards, awaiting restoration and display in the California State Railroad Museum. In early 1981 the monstrous locomotive received a cosmetic restoration in the Museum's restoration facility. It has been completely repainted and refurbished, and many of the missing parts replaced. Mechanically, the engine is in remarkably good condition; during the Museum's cosmetic restoration, nothing was found that would preclude the possible restoration of the locomotive to operable condition at a later date.
Southern Pacific No. 4294, the last one of its kind in the world, occupies a place of prominence on the main floor of the Museum of Railroad History.