Class 101 (Locobase 13907)

Data from DeGolyer, Volume 41, p. 114; and GM&N 8 - 1924 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange collection. (Thanks to Steve Low for his 20 April 2018 email providing the correct original setting of the boiler pressure and firebox heating surface area.) Works numbers were 38354-38355, 38378-38381, 38417-38418 in September 1912

Like the Pacifics supplied to the NOM & C at the same time (Locobase 2789), the eight Mikados of 1912 were built with 13" (330 mm) piston valves supplying an identical cylinder volume and actuated through outside radial valve gear. Smaller drivers suited their freight-hauling role and their boilers had three fewer tubes for some reason. In the specs, the safety valve setting was specified to be 185 psi as shown, but the 1924 diagrams show an increase of 15 psi (1.03 bar) to 200 psi (13.79 bar).

For mainline Mikados of the time, these were relatively small, lightweight engines that rolled on relatively light rail (70 lb/yard or 35 kg/metre).. Locobase 1353 shows the heavier 109-112, which arrived in 1920.

The class adopted the herald of the Gulf, Mobile & Northern in 1917, but kept their numbers.

GM & N sold the 101-104 to the Tennessee, Alabama & Gulf, which added 100 to each road number and operated 201-204. The TAG sold all 4 in 1937 to locomotive rebuilder/reseller Southern Iron & Equipment. The Sydney & Louisburg of Cape Breton in Nova Scotia, Canada, bought the quartet in 1938 and renumbered them 73, 75, 76, 74, respectively. They ended their days in 1957.

The latter four remained on the GM & N even after it was merged with the Mobile & Ohio and they kept their road numbers. All were scrapped by 1948.

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Class 109 (Locobase 1353)

Data from GM&N 7 - 1924 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. See also DeGolyer, Volume 59, pp. 423. Works numbers were 54012-54015 in November 1920.

Relatively small Mikados purchased just after the return of railroading to private ownership following World War One. The cylinders were supplied by relatively large 13" (330 mm) piston valves. Rail weight was 70 lb/yard (35 kg/metre) and the profile was very mild as it featured 1% maximum grades and 4 degrees curvature

All moved over to the Gulf, Mobile & Ohio roster while retaining their road numbers.

Three were scrapped in the late 1940s, while 111 was sold overseas.

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Class 400 (Locobase 13796)

Data from M&O 7 - 1925 and M&O 9 -1940 locomotive diagram books supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange collection. See also DeGolyer, Volume 38, pp. 279+; Volume 40, pp. 306; Volume 42,pp. 305;Volume 42, pp. Volume 50, pp.334+; Volume 51, pp. 131+ .and 141 +. (Thanks to Chris Hohl for his 31 December 2022 email noting the estimated weights in the Baldwin specs.) . Baldwin's works numbers were 37195-37198 in November 1911; 37676-37677 in April 1912; 38940-38941, 38995 in December; 40823 in November 1913; 41055 in December; 41056-41058, 41090-41093 in January 1914; 42477-42478 in September 1915; 42913 in February 1916.

Apparently encountering some of the Southern's myriad K-class Mikados (Locobase 44) induced the M&O to order four duplicates in 1911.

Later orders increased the count to 21 locomotives. According to Chris Hohl, weights in this class varied modesxtly in Baldwin's specifications according to batch as follows:

400-405: Drivers 212,300 lbs (96,298 kg); Engine - 269,000 lbs (191,416 kg)

#406-417: Drivers - 215,700 lbs (97,840 kg).; Engine - 272,940 lbs (123,804 kg).

#418-420: Drivers - 217,000 lbs (98,430 kg).; Engine - 277,000 lbs (125,645 kg)

By 1925, the M&O didn't differentiate weights among classes.

The design offered a combustion chamber and four arch tubes that contributed to the direct heating surface area shown in the specs. The boiler was set to 175 psi; by 1925, the railroad had raised the settings to 185 psi (12.07 bar)--shown in specs--and 195 psi (13.45 bar).

Although some were delivered with tenders carrying 14 tons of coal, Chris Hohl reported, ll rolled on the same weight of tender (153,000 lb/69,400 kg) initially. Later, the M&O engines trailed

The 14" (356 mm) diameter piston valves had a max travel of 6" (152 mm). Journals on third driving axle (which took the power from the main rod) in 418-420 measured 11"(279 mm) in diameter, an inch greater than the earlier locomotives..And they adopted Southern valve gear in place of the Walschaert design used in the earlier batches.

This was a class that served the M&O and its successor Gulf, Mobile & Ohio to the end of steam.

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Class 477 (Locobase 15338)

Data from DeGolyer, Vol 74, pp. 147+ . Works numbers were 59157-59159, 59170, 59172 in April 1926.

Several years after the Light Mikados designed by the United States Railroad Administration had proliferated throughout the mainline rail network, individual railroads were still ordering slight variations of this very successful locomotive. The M&O's quintet duplicated nearly every dimension and, like the light Mikes, their firebox heating surface areas included 50 sq ft (4.7 sq m) in the combustion chamber and 27 sq ft (2.5 sq m) in arch tubes. Cylinders were served by piston valves measuring 14" (356 mm) in diameter.

The one significant difference was the use of Baker gear instead of the original Walschaert valve gear. Appliances varied; for example, the Franklin power shaker (of the grate) was expressly omitted.

All served the M&O and successor GM&O into the late 1940s.