The EMD SD45T-2 is a 6-axle diesel locomotive conceived in early 1972 by EMD at the request of Southern Pacific Railroad (SP). Like the similar SD40T-2, this locomotive model was often called a "tunnel motor". 247 of this model were built from February 1972 to June 1975. Out of the total, 84 units were built for SP's subsidiary Cotton Belt. From April 1986 to December 1989, about half of the units were rebuilt and designated as SD45T-2R and 24 of the 126 rebuilds were built for Cotton Belt. The SD45T-2 is a variation of the SD45-2, with cooling system modifications. Specifically, the intake for the radiator cooling air was moved to the walkway level, and the cooling fans themselves moved under the radiator cores, instead of on top. The tunnel motors were built to perform best in superheated tunnels in mountainous areas in the western United States. These locomotive models featured air intake grills at the lower rear of the locomotives' long hoods so the engines could obtain available cool and clean air into the radiator section. The SD40T-2 is similar in appearance to the SD45T-2. One key spotting difference is that the hood is longer on the SD45T-2 to accommodate the V20 prime mover vs. the V16 used on the SD40T-2. The result is that the cab is further forward on the frame, so there is no "front porch" or "snoot" nose. This mimicks the differences between the SD45-2 and the SD40-2. Another key spotting difference between the SD45T-2 and the SD40T-2 is that the SD45T-2 has three fan access doors above the cooling air intake, while the SD40T-2 has only 2 on each side. Like the SD40T-2, some of SP's SD45T-2 tunnel motors were obtained by Kansas City Southern Railway, Bessemer and Lake Erie Railroad, Duluth, Missabe and Iron Range Railway and by the Union Pacific Railroad when it merged the SP in 1996. Some SD45T-2s were rebuilt again and designated to SD45T-3, SD40T-3 and SD40-2T, in addition, some locomotive leasing companies own the SD45 tunnel motor locomotives. They are found scattered all over the United States and are an increasingly rare sight. As of January 2003, the trademark SD45T-2R tunnel motor, SP#6819 (formerly SP 9193) was donated to the California State Railroad Museum in Sacramento.