Caledonian Railway 721 Class

The "Dunalastair" class marked a new era of development in late-Victorian British steam locomotive design.[2] The average weight of passenger trains had greatly increased in the 1880s and 1890s due to the demand for more comfortable, better-appointed and safer carriages.[3] Combined with continually rising passenger volumes and the competition between railway companies to offer faster services and locomotive engineers were faced with producing engines that could operate longer, heavier trains at faster speeds. The existing pattern of inside-cylinder 4-4-0 express engine was reaching the limits of its development and many railways were resorting to the inefficient practice of double heading to maintain schedules.[4]

McIntosh provided the solution with the original "Dunalastair" of 1896. In broad design this was identical to the conventional 4-4-0 engine drawn up by his predecessor Dugald Drummond,[2] but it carried a boiler significantly larger than was usual for the time - almost to the full limits that the Caledonian's loading gauge would allow, operating at a relatively high pressure of 160 psi (1,103 kPa). The boiler also contained more fire tubes of a greater diameter than its predecessors, greatly increasing its steam generating capacity and overall steam volume. While the top speed of the 721 Class and its developments was largely the same as other express 4-4-0s the more productive and capacious boiler meant the type offered a hugely improved ability to maintain high speeds with heavy loads on steep gradients, allowing the "Dunalastairs" to set high average speeds over the Caledonian's arduous main line over Beattock Summit.[2] So confident was McIntosh that his new engine would do away with the need for double heading that the "Dunalastairs" were originally built without brake hoses on their front buffer beam, meaning that a second engine could not be coupled to them.

The principles of the 721 Class and its boiler were adopted by many other locomotive engineers and railways in the 1890s and early 20th century, leading to the so-called 'big engine' period of design. Other engine classes such as the GNR Class C1 and the GWR 4100 Class were inspired by the success of the "Dunalastairs".[2]

The class was very successful and developed in four different versions:[5]

• Dunalastair I (721 Class) built 1896
• Dunalastair II (766 Class) built 1897 (some rebuilt with superheaters 1914)
• Dunalastair III (900 Class) built 1899–1900 (some rebuilt with superheaters 1914–18)
• Dunalastair IV (140 Class) built 1904–10 (some rebuilt with superheaters 1915–17)

The rebuilding with superheaters was accompanied by a reduction in boiler pressure and an increase in cylinder diameter.

There are two further classes of McIntosh 4-4-0 locomotives which some authors have included in the Dunalastair series. These are:

• 139 Class, built 1910–12 with Schmidt superheaters
• 43 Class, built 1913–14 with Robinson superheaters

During the national coal strike of 1912, some Caledonian locomotives, including Dunalastairs or 139 class engines, and two engines from class 812[1] were fitted with Holden oil burners for a short time. They received a 520 imperial gallons (2,400 L) fuel tank atop the tender and more refractory bricks in the firebox.[6]

• On 22 May 1915 three of these locomotives, no. 121 of the 139 Class, no. 140 of the Dunalastair IV Class and no. 48 of the 43 Class, were involved in the Quintinshill rail disaster. A down local train from Carlisle (hauled by no. 907, a 4-6-0 of the 903 Class) had been crossed from the down line to the up line in order to allow a late-running down express from London Euston to pass it. An up troop train from Larbert, hauled by no. 121, was incorrectly given clear signals and collided with the stationary local train, and the express from London, double-headed by nos. 140 and 48, then collided with the wreckage of the first collision.[8] One of them, no. 121 was damaged beyond repair by the impact and scrapped whilst the other two were repaired.
• On 25 October 1928, locomotive No. 14435 was one of two hauling an express passenger train that was in a rear-end collision at 60 miles per hour (97 km/h) with a freight train at Dinwoodie, Dumfriesshire due to errors by the guard of the freight train and the Dinwoodie signalman. Four enginemen were killed and five people were injured.[9][10]

Table 1

Table 2

The 139 Class and 43 Class are included in the Dunalastair series by some authors. Some locomotives survived into British Railways (BR) ownership in 1948.[11][12][13][14]

SNCB-NMBS Class 16

Belgian State Railways (SNCB-NMBS) derived six series of steam locomotives (424 units) from the Dunalastair design between 1899 and 1913:[15][16]

• Type 17 – regular 4-4-0 Dunalastair III design: driving wheel 1.98 m, 52.5 tons (built 1899–1901, 95 units, including five supplied by Neilson Reid)
• Type 18 – more powerful than Type 17: 53.3 tons (built 1902–05, 128 units)
• Type 19 – (initially Type 18S): superheated version of type 18: 57.8 tons (built 1905, 6 units)
• Type 20 – (initially Type 18bis): upgraded (superheated and more powerful) type 18: 60.0 tons (15 units)
• Type 14 – (initially Type 15bis): 4-4-2T tank locomotive based on Dunalastair III design: driving wheel 1.8 m, 62.0 tons, deep firebox (built 1900–01, 49 units)
• Type 15 – same as Type 14, but with mid-deep firebox: 64.0 tons (built 1900–08, 73 units)
• Type 16 – (initially Type 15S) superheated version of Type 15 with mid-deep firebox : 69.4 tons (built 1905–13, 78 units)

Two of them are preserved in cosmetic state by SNCB: 4-4-2 tank locomotive 16.042 and express locomotive 18.051.[17][18]

18.051 also features an eight-wheel tender similar to the Caledonian eight-wheel tender. This kind of tender was used on Type 17 and some of the first Type 18 while the rest (including 18.051) had wider and larger six-wheel Belgian tenders. That one was salvaged when 18.051 was restored and was originally built for an older Type 18.

The first Dunalastair to be withdrawn from service, other than for accident damage, was 14343 in 1933. The reason for its withdrawal is unclear. The next withdrawal was not until 1937. By 1944 only five members of the 900 Class remained. The last 900 Class survivor received the British Railways number 54434 and was based at Aviemore until it was withdrawn in 1948.[19] None have survived to preservation.

• Locomotives of the Caledonian Railway

• Allen, Cecil J, ed. (1948). The ABC of British Locomotives. Vol. 3, 40000–59999 Steam Locomotives: London Midland Region Scottish (ex. LMS) Region. London: Ian Allan.
• Baxter, Bertram (1984). Baxter, David (ed.). British Locomotive Catalogue 1825–1923. Vol. 4: Scottish and remaining English Companies in the LMS Group. Ashbourne: Moorland Publishing. pp. 85–87.
• Casserley, HC; Johnston, SW (1966). Locomotives at the Grouping. Vol. 3: London Midland and Scottish. London: Ian Allan. pp. 138–144.
• Cornwell, HJ Campbell (1974). Forty Years of Caledonian Locomotives, 1882–1922. Newton Abbott: David & Charles. ISBN 0-715365339.
• Dunbar, AG; Reed, B (1973). Caledonian 4-4-0s. Locomotive Profiles. Vol. 34. Windsor: Profile Publications.
• Earnshaw, Alan (1991). Trains in Trouble. Vol. 7. Penryn: Atlantic Books. p. 21. ISBN 0-906899-50-8.
• Ellis, Hamilton (1959). British Railway History. Vol. 2. London: George Allan & Unwin.
• Essery, R; Jenkinson, D (1986). LMS Group Locomotives. Vol. 3: Absorbed Pre-Group Classes, Northern Division. Poole: Oxford Publishing Co. ISBN 0-860932664.
• MacLeod, AB (1948) [1944]. The McIntosh locomotives of the Caledonian Railway, 1895–1914. Famous Locomotive Types. London: Ian Allan.
• Nock, OS (1968). The Caledonian Dunalastairs and Associated Classes. Newton Abbott: David & Charles. ISBN 0-715342517.
• Nock, OS; Cooper, BK (1992) [1966]. Historic Railway Disasters (4th ed.). London: Book Club Associates. pp. 88–90, 92. ISBN 0-711017522. CN 6843.

• Smellie, Jim. "Caledonian Railway Class 4-4-0" (PDF). Caley Coaches Ltd.
• "Caledonia Railway Dunalastair I – IV". Eisenbahn in Großbritannien (in German). Archived from the original on 16 December 2014. Retrieved 28 June 2012.