The P&P owns a MTH Santa Fe FT and the question came up "What does FT stand for?" An internet search yielded that the "F" stands for freight and the T was for 2700 horsepower with a two unit set. It was first made in 1939 and 1096 units were made, 320 of which went to Santa Fe. Production of F unit varients ended in 1960 with a total of over 7600 units (A and boosters) produced. The F is the top selling cab unit of all time.
For more details go to http://exotic.railfan.net/F.htm