In 1925, the Baltimore & Ohio Railroad built its first "Mountain" locomotive
(road number 5500) using the boiler from number 6009, a Baldwin built Class S
2-10-2. A year later. the B&O built another (road number 5501) using the
boiler from number 6030. These two locomotives were designated Class T and
had 30 x 30 cylinders, 74" drivers, and a 220 psi boiler pressure which
resulted in a tractive effort of 68,200 pounds. They weighed 400,000 lbs and
worked on the west end of the Cumberland Division pulling passenger trains
until retired in 1953.
In 1930, George Emerson, the General Superintendent of Motive Power &
Equipment wanted to prove his theory that a water-tube firebox was
practical. He had the B&O order two "Mountain" type locomotives from the
Baldwin Locomotive Works, one (Class T-1, road number 5510) equipped with a
water-tube firebox and the other (Class T-2, road number 5550) with a
conventional type firebox. These two locomotives were identical except for
their fireboxes and had 27.5 x 30 cylinders, 74" drivers, a 250 lbs boiler
pressure and exerted 65,000 lbs of tractive effort. Number 5510 weighed
384,000 lbs and number 5550 weighed 1,000 lbs more. Emerson wanted to
operate the two locomotives in similar service and then compare operating and
maintenance costs. This experiment was never completed and the two
"Mountains" were used until the early 1950s.
In the early 1940s, the B&O decided to build "Mountain" type locomotives to
help with the increase in traffic caused by the war effort. From 1942 to 1948
it built forty of them (Class T-3, road numbers 5555 through 5594) in its
Mt. Clare Shops in Baltimore, MD. These locomotives were built to the same
general specifications which included 27 x 32 cylinders, 70" drivers, a
boiler pressure of 230 psi, a tractive effort of 65,100 lbs and a weight of
375,000 pounds. There were some variations in the features of these
locomotives as shown in the chart below. The Class T-3s were retired in
The B&O bought thirteen 4-8-2s from the Boston & Maine. They were given road
numbers 5650 through 5662 and were designated as Class T-4 and were used
There are no surviving B&O "Mountains". The Class Ts (numbers 5500 & 5501)
were scrapped in 1953. Class T-1 number 5510 was scrapped in 1951 and Class
T-2 number 5550 was scrapped in 1952. Some of the Class T-3s and T-4s were
scrapped in the early 1950s. In 1957, all of the remaining T-3s and T-4s
were renumbered in the 700 series. The T-4s were retired in 1958 and the
T-3s lasted a little longer, but by 1960 all of the B&O "Mountain" had been
Class T (Locobase 196)
Data from tables in 1930 Locomotive Cyclopedia and B&O to 1954 Assorted Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Raildata collection.
Firebox heating surface included 42 sq ft (3.9 sq m) of arch tubes.
Two engines built by the B&O using class S 2-10-2 boilers (Locobase 1036) on a shorter wheelbase. The 5500 had 29" (737 mm) diameter cylinders while the 5501 had the square dimensions shown in the specs. They also had 14" (356 mm) piston valves instead of the 16" (406 mm) valves feeding the 2-10-2s.
Although 74" drivers promised a good dual-role engine, the B&O did not follow up on this design, possibly because the boiler was in fact too long for a four-axle driving layout. Both retired in 1953.
Class T-1 (Locobase 3097)
Data from B&O Staufer Locomotive Diagrams (Medina, Ohio: Alvin Stauffer), p. 94 supplied in May 2005 by Allen Stanley from his extensive Raildata collection. Works number was 61569 in November 1930.
One of two Mountains built by Baldwin in 1930 to test the Emerson watertube firebox alongside a conventional stayed firebox. In the Emerson, a 40" diameter drum ran along the centerline over the grate and from front sheet to back head. Headers at the top and bottom of the firebox were connected by two rows (190 tubes total) of 2 1/2" diameter water tubes. The top header was joined to the drum by 13 4"-diameter nipples on each side.
The value of the Emerson firebox was held to be the much greater heating surface it offered to the fire. From 474 sq ft of evaporative surface, including syphons, in the stayed firebox, the surface expanded 82% to 866 sq ft in the Emerson (including the 83 sq ft of arch tubes).
Unfortunately for such designs, the system was prey to vibration, insufficient insulation, maintenance headaches. Moreover, it didn't after all offer much of an advantage. The T-1 and the articulated KK-1 were the only watertube engines supplied to the B&O.
Class T-2 (Locobase 3098)
Data from B&O Staufer Locomotive Diagrams (Medina, Ohio: Alvin Stauffer), p. 95 supplied in May 2005 by Allen Stanley from his extensive Raildata collection. Works number was 61554 in November 1930.
This was the conventional, stayed firebox variant of the Mountain tested by the B&O against the T-1 (Locobase 3097), which had a watertube firebox. As part of the firebox heating surface, the T-2 had 18 sq ft (1.65 sq m) of arch tubes and 95 sq ft (8.8 sq m) of thermic syphons.
Like the T-1, the T-2 soldiered on solo until 1951.
Class T-3b/T-3c (Locobase 193)
Data from B&O to 1954 Assorted locomotive diagrams supplied in May 2005 by Allen Stanley from his extensive Raildata collection.
Similar T-3b class numbered from 5565-5594. 40 locomotives built by the B&O from 1942 to 1948 using boilers from retired 4-6-2 and 2-8-2 engines. The frame was cast steel with integral cylinders. The shops fitted several different fireboxes to engines in this class. One was a 363 sq ft (33.7 sq m) unit that included 35 sq ft (3.25 sq m) of arch tubes and 14 sq ft (1.3 sq m) in a single thermic syphon. The second added the syphon and 49.9 sq ft (4.65 sq m) of circulators to the basic 314 sq ft (29.17 sq m) of grate surface. The third added one more circulator to bring the total to the 388 sq ft shown in the specs. A fourth, apparently mounted only on certain T-3Bs, added 72 sq ft (6.7 sq m) of circulators to the grate area and achieved the same firebox heating surface area.
Last T-3 retired in 1960.