Maine Central Railroad Class M locomotives were originally intended for heavy freight service.
The oldest of the class surviving past United States Railroad Administration operation were Portland Company builders numbers 606 and 607 built in 1890.
The longest surviving representatives of the class were three built by "Schenectady" in 1897, as Portland and Rumford Falls Railway numbers 10 through 12.
[1] These three were rebuilt with higher-pressure boilers in Maine Central's Waterville shop between 1914 and 1921 as sub-class M-5.
[2] These reboilered locomotives with 25,000 lbf (111.2 kN) tractive effort were numbered 246 through 248.