The two whalebacked M-4s I referred to each had different sizes of whalebacks. Unfortunately, I don't have information on their classification. Both are larger than the whaleback in the above which is a "squashed" variant. "My" picture of M-4 1644 taken in November 1946 at Los Angeles shows a "normal-looking" whaleback tender at least as tall the the loco's boiler. Picture of M-4 1685 taken in June 1953 at Roseville has a very large whaleback where the fuel section is of slightly larger diameter than the water section and is at least as tall as the cab roof.
There may have been more variants, but the whalebacks I remember are the 73SC-1, 98SC-1 and the 120SC-1. IIRC, it was the 120SC type that had the oil bunker of a larger diameter than the water cistern. I'm not sure, but that may have been a result of rebuilding the oil bunker to increase capacity. Some of the 73SC's were originally built for SP's Vauclain compound A-1 4-4-2's from what I remember. Unfortunately, my copy of Arnold Menke's compilation of SP tender diagrams is back in California, so I'm limited to memory. As I recall, some, if not all of the B-1 2-8-4's purchased second hand from the B&M got 120SC tenders when they were converted to oil.
For those of you who are not SP fans, SP's tender classification was quite simple. The numbers indicated water capacity in the nearest 100's of gallons, the letters indicated whether the tender was rectangular, cylindrical or semi-cylindrical ("whaleback") and the number after the dash indicated the series. For example, a 160C-3 tender was of 16,000 gallon capacity, cylindrical , third series. Spectrum's "Hicken" (misnomer) is an example of a 160C-x tender. Their "medium" Vanderbilt appears to me to be a 9,000 gallon tender (90C-x) as the 10,000 gallon Vandies were a bit longer. The tender that comes behind the IHC 2-6-0 is a 52R-x tender (5200 gallon Rectangular) that was lengthened by Pemco to accommodate the tender drive. Model Die Casting's short Vandy is a 70C (7000 gallon) tender.
SP tenders are an interesting study in and of themelves. They had quite a variety, not only those built new for SP, but also the tenders which came with second hand engines.
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