Class I-1 (Locobase 9045)

Data from C&A 6-1918 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection. Works number for this single locomotive was 21476, produced in January 1903

This was an early Pacific that can nicely illustrate the difference between an Atlantic and a Pacific. Locobase 4096 shows the 1901 E-1 4-4-2s. Compared to that set of Atlantics, the I-1 had a nearly identical firebox, cylinders only 2" greater in diameter (and supplied through similar 12" piston valves), but tubes lengthened by 4 ft (and their number increased by about 2 dozen), and an extra axle of adhesion.

This same locomotive would be superheated; see Locobase 9046.

Class I-1 - superheated / P-10 (Locobase 9046)

Data from C&A 6-1918 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection. Note: all of the C & A diagrams for superheated Pacifics with 28-element superheaters show 851-sq ft superheater areas. Locobase has adjusted that number to 651 sq ft as it fits not just other 28-element superheater measurements but also is in line with the 745 sq ft of the 32-element superheaters in the I-4s.

Both early Pacifics underwent a superheating makeover that confined itself to redoing the boiler; this entry refers to the 73" diameter variant. The usual subtraction from the total tube number in favor of flues occurred, but was accompanied by an unusual reduction in tube diameter at the same time. The firebox now showed 29.7 sq ft of arch tubes as contributing to firebox heating surface. The engine still had its 12" piston valves.

Class I-2 (Locobase 9047)

Data from C&A 6-1918 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection. Works number for this single locomotive was 21487, produced in January 1903

In the same month that Baldwin built the 73"-drivered I-1 (Locobase 9045), it also produced this express passenger version. The grate remained the same size, as did the cylinders (with their 12" piston valves), but the boiler contained 50 fewer tubes.

The I-2 was superheated; see Locobase 9048.

Class I-2 - superheated / P-11 (Locobase 9048)

Data from C&A 6-1918 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection. Note: all of the C & A diagrams for superheated Pacifics with 28-element superheaters show 851-sq ft superheater areas. Locobase has adjusted that number to 651 sq ft as it fits not just other 28-element superheater measurements but also is in line with the 745 sq ft of the 32-element superheaters in the I-4s.

Although the saturated version of this design was quite different from the I-1 (Locobase 9045), the superheated conversion resulted in a locomotive whose only differences were the taller drivers and a greater adhesion weight.

Class I-3 - superheated / P-12 (Locobase 9049)

Data from C&A 6-1918 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection. Note: all of the C & A diagrams for superheated Pacifics with 28-element superheaters show 851-sq ft superheater areas. Locobase has adjusted that number to 651 sq ft as it fits not just other 28-element superheater measurements but also is in line with the 745 sq ft of the 32-element superheaters in the I-4s.

In superheating the Harriman Pacifics (Locobase 5313), the Alton installed its standard 28-element superheater assembly that included a reduction in tube count as well as individual tube diameter. Because the Harriman's had smaller boilers to begin with, the result was a high degree of superheat that undoubtedly increased their power.

Class I-4 (Locobase 4199)

Oddly proportioned Pacific profiled in the 2 October 1908 Railroad Age Gazette. The grate seems much too small for the boiler, although the relatively small cylinders kept the grate demand factor reasonable. An article in the October 1908 American Engineer & Railroad Journal comments that "has the largest ratio ...of heating surface to grate area in our records."

It's odd that the adoption of the Pacific layout didn't lead to a wider grate. (Drury - 1993 - comments on the narrow firebox, but ascribes 22"cylinders to this batch, which the RAG clearly shows had 23" pistons.)

RAG's equivocal prediction was"...these are high-powered machines for passenger service, and as the design has been worked out in light of experience with locomotives built some time ago, the performance should be satisfactory."

These were later redesignated P-13a, and superheated; see Locobase 9050.

Class I-4A - small grate / P-13 (Locobase 9050)

Data from C&A 12-1924 and 1 - 1930Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection.

The superheated I-4 Pacifics retained the narrow firebox they had when originally delivered as saturated-steam engines. A later update would remove the boiler with the small grate and replace it with the one used by the I-5 engines. Even in 1930, however, 2 of the 5 -- 605 & 609 -- would still be using the narrow grate.

Class I-5 - 77"" drivers (Locobase 9051)

Data from C&A 6-1918 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection.

These were the first five locomotives of a 15-engine order from Brooks. They had the tallest drivers of any Alton class, 14" piston valves, and the Harriman-Pacific size grate. See Locobase 9051 for the 77"-drivered variant.

Class I-5 - 80"" drivers (Locobase 9052)

Data from C&A 6-1918 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection.

These were the first five locomotives of a 15-engine order from Brooks. They had the tallest drivers of any Alton class, 14" piston valves, and the Harriman-Pacific size grate. See Locobase 9054 for the superheated variant.

Class I-5A - 77"" / P-15 (Locobase 9053)

Data from C&A 1 - 1930 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection.

The two sub-variants of the I-5 class went into service as saturated steam locomotives; see Locobases 9051-9052.

When the Alton's 4-6-2s were superheated, the I-5s remained divided into two subgroups based on driver diameter. They were otherwise identical except for a 5,500-lb difference in adhesion weight in favor of the 77"-driver engines shown here.

This class had some free-steaming qualities inherent in a relatively large boiler and 14" piston valves, but the Harriman Standard grate area may have prevented a full exploitation of a decent amount of superheat.

Class I-5A - 80"" / P-14 (Locobase 9054)

Data from C&A 1 - 1930 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection.

See Locobase 9053 for comments on the superheating of this HCS design.

Class I-6 / P-16 (Locobase 7584)

Data from reproduction of 1913 Alco Bulletin 1016 on Richard Leonard's http://www.railarchive.net/alcopacifics/index.html (accessed 16 June 2006).

These Harriman Pacifics were the equivalent of the Southern Pacific's P-6 class. Drury (1993) notes the tapered boiler course that joined the extended firebox to the front course. Although they were delivered as long ago as 1913, this decade of locomotives was the last new passenger power the Alton would buy. Drury notes that a 1943-1944 upgrade included a new superheater, Nicholson thermic syphons, and Worthington feedwater heaters.

Class P (Harriman)/I-3 (Locobase 5313)

Taken from a table in July 1904 American Engineer & Railroad Journal. Baldwin appears to have taken the firebox of the E-1 Atlantic that immediately preceded it and attached to it a longer boiler less densely packed with tubes. At the same time, cylinder diameter grew by 2 inches. The result was a design that put 30,000 more lb on the drivers.

Drury (1993) says these were Harriman Pacifics. They entered service with Stephenson gear and inside-bearing trailing trucks, but were later fitted with outside Walschaerts valve gear and outside-bearing trucks.