Although the Milwaukee Road had already procured its first few Pacifics in 1893, the Atlantics had still to pull the fastest trains for the time being. However, when they got problems with trains of ten to 14 cars, the 70 class F3 Pacifics were ordered from ALCO in 1910. They were initially operated with saturated steam and were retrofitted with superheaters from 1920 onwards. The diameter of the cylinders was increased from 23 to 23.5 inches, and for six of them even to 24 inches.

No. 152 with retrofitted streamlining in November 1953 in Madison, Wisconsin

collection Taylor Rush

The locomotives were considered very powerful and well balanced. If necessary, they could reach up to 90 mph or 145 km/h. It wasn't until 1940 and 1941, when the Milwaukee Road was already using Hudsons, that three were rebuilt into the F3-as. The grate was widened and its area was significantly increased, but the direct heating surface of the firebox only grew slightly. Two of them were given streamlined fairing to pull the “Chippewa”.