NEVER MIND THE RETROSPECTIVES, LET'S BUILD SOMETHING NEW. The Superintendent has brought to your attention a number of British projects to re-create historic steam locomotives from the past, many of which went to the cutter as recently as 1969. Word has now reached the Superintendent's office, by way of Railway's steam news section, of an advanced-technology steam locomotive project called the 5AT (the equivalent in some aspects of a Standard Five Ten-Wheeler, using advanced technology.)

I see they're envisioning a proper tender.
View some development notes here.

Note the homage to Argentina. The project designers intend to run their creation at 125 mph, and here their education is incomplete.
The only steam locomotives required to operate (transitorily) at 100 mph to maintain schedules were the Milwaukee Hiawatha 4-4-2's and 4-6-4's, and perhaps the DR 05 4-6-4's. These and a few other classes have reached transitory speeds of ~125 mph on test. The 5AT is being designed for continuous 125 mph capability with a 112.5 mph (180 km/h) continuous operational speed.
I'm looking at a table on p. 70 of The Hiawatha Story (no price comparison available, my copy is not for sale) headlined Up, Up ... Past 100. The author is E. L. Thompson of Railroad, who has some familiarity with British speed log formats.
Chicago, Milwaukee, St. Paul + Pacific; train No. 6; Tuesday, January 14, 1941; nine cars, 430 tons(*). F-7 Hudson No. 100 -- tractive effort, 50,300 pounds; drivers, 84 inches; cylinders, 23 1/2 x 30 inches; boiler pressure 300 pounds.
The reader only need note the following observation.
Note that the magic 100 mark was first touched at the third milepost past Tower A-68 [just south of Caledonia, Wisconsin - SHK]; and from a mile past Sturtevant, 31 consecutive miles were timed at 100 mph or better (emphasis in the original). The slow order [permanent way slack -- SHK] over the temporary detour interrupted this string of three-figure speeds, but starting again at Northbrook, 8 of the succeeding 11 miles were also covered in the 100s.
This train departed Milwaukee three minutes late on a 75 minute schedule, arriving Chicago 2 1/2 minutes to the good, in a snowstorm.

The people working on the 5AT project have one other objective to meet. A test run of the recently deliverered Hiawatha equipment on May 15, 1935, using the Two-Spot, a Hiawatha Atlantic, maintained 112 1/2 mph "without difficulty" for 14 miles, probably somewhere between Columbus and east of the Wisconsin Dells, where there are some speed restrictions account curves and a bridge over the Wisconsin River.

The "required to operate" language is accurate, as a 75 minute Milwaukee-Chicago service is an average speed of 68 mph start to stop, but the Hiawatha steam power had the ability to sustain these speeds over great distances if called on to do so. The diesels that replaced them also had the ability, but that's a story for another day.

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