The P-3a class of B&M Pacifics was a 1923 product of the American Locomotive Company. With 73-inch drivers and cylinders of 24x28 inches, these locomotives sustained 200 p.s.i. of boiler pressure. They weighed 267,700 pounds minus tender and developed 37,558 pounds of tractive effort. Other dimensions are given in the commentary for No. 3709. This image of No. 3700 comes from the collection of Carl Weber. It was snapped at Reading, Massachusetts in March 1951 by Bruce Black, two years before the locomotive was retired.