The GE U36B was the last and most powerful 4-axle Universal model the company produced. By the time of its production in the late 1960s GE must have realized that interest for powerful 4-axle road switchers was rapidly declining, as the final sales numbers bore out, with only three roads purchasing the U36B (and only two ultimately used the locomotive in revenue service). With the relative unsuccessful sales numbers of the U36B, GE instead began focusing its efforts on six axle models. Despite the model's poor sales performance it actually became quite famous, particularly among railfans, for its use as power on the Auto Train which debuted in the early 1970s. The service was a privately-funded and managed operation. Its trademark was allowing passengers to take their automobile with them when traveling from Virginia to Florida. The idea worked although the Auto Train later foundered.
The service, however, was retained by Amtrak. Today, despite these units being rather rare there are still a handful in operation; Nashville & Eastern #5772 is originally Seaboard Coast Line #1820 while Transkentucky Transportation operates nine former SCL units. These include original SCL numbers 1775, 1777, 1783, 1807, 1812, 1838, 1841, 1843, and 1847.
The GE U36B began production in January, 1969 offering a hefty 3,600 horsepower (utilizing the builder's 4-cycle model FDL16 prime mover), one of the most powerful 4-axle road switchers any locomotive builder ever produced. As GE advanced its locomotive development the U36B, outwardly, began to resemble what would become newer locomotives like the "Dash 7" series, particularly with the flared rear radiator design which first appeared on the U33B. Today, this feature remains a classic GE trademark. In any event, the U36B was the second-to-last Universal series model to enter the company's catalog, as only the U36C was cataloged later in 1971. It was certainly the final four-axle U-boat to enter production as General Electric looked to only focus on six-axle designs, as its late model C-C U-boats sold very well (more than 1,000 were outshopped).
While the flared radiator was a new feature on GE locomotives the U36B mostly still resembled earlier 4-axle road switchers with boxy carbody designs and straightforward engineering that allowed for generally ease of maintenance. As GE's last 4-axle Universal model the U36B sold relatively poorly with just 125 units built by the time production had ended in December, 1974. The Seaboard Coast Line purchased the most, 108, and the Auto-Train Corporation ordered another 13 (Conrail ordered 4 for use by Auto-Train but these were never delivered). One interesting note about the U36B, and all of GE's four-axle U-boats is that the company never elected to increase the tractive effort rating of the models even as it continued to build more powerful models.
The Seaboard Coast Line's 103 models remained in use through the CSX Transportation merger of the 1980s. The company had mostly retired the fleet by the early 1990s and sold the units to various short lines (like those mentioned above). Interestingly, the Transkentucky, which owns the most U36Bs, also operates several units of GE's U28B design, one of the railroads to still employ the locomotive in freight service. In any event, as the remaining U36Bs continue to age some will probably find their way into museum collections for preservation. Lastly, for more information about the GE U36B and total production numbers of units built please refer to the chart below.
For more reading about GE's U-boat line the book U-Boats: General Electric's Diesel Locomotive by author Greg McDonnell provides a complete history of the company's first production diesel models. Also, noted historian Brian Solomon has authored a number of books covering the history and background of GE's locomotives. Two, which provide a general but thorough coverage include GE Locomotives and GE And EMD Locomotives: The Illustrated History. As with virtually all of Mr. Solomon's you can expect a well-written title with large, crisp, and sharp photographs.