GER Decapod

GER Class A55
Type and origin Power type Steam Designer James Holden Builder Stratford Works Order number A55 Build date 1902 Total produced 1
Specifications Configuration: ​  • Whyte 0-10-0WT  • UIC E n3t Gauge 4 ft 8 1⁄2 in (1,435 mm) Driver dia. 4 ft 6 in (1.372 m) Loco weight 80 long tons 0 cwt (179,200 lb or 81.3 t) Fuel capacity 2 long tons 0 cwt (4,500 lb or 2 t) Water cap 1,300 imp gal (5,900 l; 1,600 US gal) Firebox:  • Firegrate area 42 sq ft (3.9 m2) Boiler length: 15 ft 6 in (4.724 m) inside dia: 5 ft 3 in (1.600 m) Heating surface 2,873.3 sq ft (266.94 m2)  • Tubes 395 x 1.75 in (44.5 mm) dia  • Firebox 131.7 sq ft (12.24 m2) Cylinders Three Cylinder size 18.5 in × 24 in (470 mm × 610 mm)
Performance figures Tractive effort 38,788 lbf (172.54 kN)
Career Operators Great Eastern Railway Class A55 Number in class 1 Numbers 20 Nicknames Decapod Disposition Rebuilt in 1906 as 0-8-0 and later scrapped

GER Class A55R
As rebuilt to an 0-8-0
Type and origin Power type Steam Rebuilder Stratford Works Rebuild date 1906 Number rebuilt 1
Specifications Configuration: ​  • Whyte 0-8-0  • UIC D n2 Gauge 4 ft 8 1⁄2 in (1,435 mm) Driver dia. 4 ft 6 in (1.372 m) Wheelbase 23 ft 3 in (7.09 m) Length 56 ft 11 in (17.35 m) over buffers Loco weight 54 long tons 6.75 cwt (121,700 lb or 55.2 t) Tender weight 38 long tons 5 cwt (85,700 lb or 38.9 t) Total weight 92 long tons 11.75 cwt (207,400 lb or 94.1 t) Boiler Inside length: 12 ft 11 3⁄4 in (3.956 m) Diameter: 4 ft 9 in (1.448 m) Boiler pressure 180 psi (1.24 MPa) Heating surface 1,869 sq ft (173.6 m2)  • Tubes 1,738 sq ft (161.5 m2)  • Flues 22.9 sq ft (2.1 m2)  • Firebox 131 sq ft (12.2 m2) Cylinders Two, outside Cylinder size 18.5 in × 24 in (470 mm × 610 mm)
Career Operators Great Eastern Railway Numbers 20 Scrapped 1913

The GER Class A55 or Decapod was an experimental steam locomotive with an 0-10-0T wheel arrangement designed by James Holden for the Great Eastern Railway. It was the first ten-coupled steam locomotive in Great Britain.

The locomotive was built for purely political purposes in order to block the passage through Parliament of a new rival scheme for an electric railway. The Decapod was built in 1902 to a design by the GER Chief Draughtsman, Fred Russell under the supervision of the Chief Superintendent, James Holden. The aim was to demonstrate the ability of a steam locomotive to accelerate passenger trains at a rate comparable to electric traction and the electric trams with which the GER was also in competition over short distances.

The locomotive was far larger than any locomotive previously built in Britain for home service. It had 10 four-foot-six-inch driving wheels, which gave high tractive effort. Three cylinders were used because there was insufficient room for two cylinders large enough to develop the required tractive effort without going up to a higher boiler pressure. Even so, it still had to have a pressure of 200 psi (1,378 kPa) to achieve the required result.

There were three separate grates and ash pans, one on each side outside the frames and a third between, giving an aggregate area of 42 sq ft (3.90 m²). The trailing drivers were given a side play of 0.5 in (12.7 mm), the coupling rods being fitted with ball and socket joints. As the cranks of the three cylinders were set at 120 degrees in relation to each other, perfect balancing of the reciprocating parts was secured. In order to minimise the drivers slipping, compressed air sanders were fitted.

The specification required that the locomotive should accelerate 315 ton (305 tonne) train from a stand to 30-mile-per-hour (48 km/h) in 30 seconds. According to Ahrons, "Holden's engine actually accelerated a new train of 18 carriages weighing 335 tons (340 tonnes) at a rate of 1.4 feet/second in very windy weather".