The General Electric Universal Series (often nicknamed "U-Boats" by most enthusiasts) is a series of four-axle and six-axle diesel locomotives built between the mid-1950's to the early-1970's. They were very reliable (despite numerous malfunctioning issues which were reported on later units per CSX and preceeding ancestors which were the original owners), and were built to compete with ALCO, EMD, and Baldwin. After the closure of the ALCO, Fairbanks-Morse, Erie, and Baldwin locomotive companies, GE became arch rivals with EMD; thus, the Universal Series being the main competition to EMD's 567 and 645-engined diesel locomotives (such as the GP35 and SD40-2).
The Southern Pacific, New York Central and Norfolk And Western purchased large fleets of early U-Boats.The U25B, introduced in 1959, was the first of the series aimed at the domestic American market.
The series itself has had more versions of diesel locomotives built than any other series by any other US-based manufacturing company (besides from the EMD SD "Super Duty" series units, even though most rebuilt versions aren't or weren't officially built by EMD; such as the B&O SD20-2.)
There are many different types of locomotives that the Universal Series consists of.
The main ways of classifying each type would be by:
- "B" meaning four axle
- "C" meaning six axle
- and the number often meaning the horsepower rating.
- U5B (Foregin)
- U18C1 (Foreign)
- P30CH (Cowl-bodied; only U-Boat to be enclosed with such form)
The GE U-Boats are often confused for their externally similar Dash 7 counter-parts. The main differences in distinguishing them from one another, is the simple fact that the Dash 7 Series locomotives have rear radiator "fins" as opposed to the U-Boats having flat rear radiators.
The U25B served as the most commercially successful type of U-Boat attracting attention from the Norfolk And Western; which began as the basis of their "high-hood" style of early "safety-cab" diesel locomotive fleets, which were eventually inherited from the Southern Railroad.
The GE "XR" Series was initially part of an early basis for the later succeeding "Dash 7" series of diesel locomotives built by GE from around 1972 to 1975, and the "XR" series itself was practically GE's response to their rival EMD's "Dash 2" line of upgraded and improved types of diesel locomotives using the ever-popular (yet failure-prone) 645-series engine.
Several "XR" Series U30B units (or pre-Dash 7); units built with longer warranties, were sold to the SLSF (Saint Louis And San Francisco, or simply "Frisco") railroad in 1972, while other models (such as the U30C-XR) were eventually sold to the Louisville And Nashville (L&N) railroad and Rock Island much later.
Most later-production (or post-production) U-Boat units produced shortly before the Dash 7's introduction (such as the U30B and later U36B; besides their six-axle counter-parts) were initially part of the "XR" Series; yet the "XR" Series itself didn't have any external differences, but rather many numerous internal differences (like the SD40-2).
The "XR" Series itself, was also similar to GE's early "Super 7" Series which was developed as the original basis for the Dash 8 line.