This locomotive was the last working example of a type which derived from a Patent granted to Robert Stephenson in 1841; he attempted to increase steam production by lengthening the boiler but he retained a short wheelbase by placing the firebox behind the third axle.

Stephenson aimed to equal the power of locomotives on Brunel's Broad Gauge lines within the restriction of his father's Standard Gauge system.

When they were used on passenger trains long-boiler designs swayed violently from side to side and from the late 1840's they were only built for freight work.

Collieries and Iron Works continued to need powerful short-wheelbase designs and (for the private railways of the North East in particular) long-boiler tank engines continued to be built

Kitson & Co. of Leeds supplied four saddle-tank long-boiler locomotives to Consett in 1872 but A No 5 & A No 6 were the first of an enlarged version in which shallow side-tanks were fitted; their resemblance to Great Western Railway locomotives has led to their being erroneously described as pannier-tanks.

Cylinders 17 1/2" x 26"                        Wheels 4' 2" diameter
Boiler 4' 0" diameter                             Wheelbase 10' 9"
Boiler Barrel 13' 10" length                   Water Capacity 952 galls.
Boiler Tubes 151 no. x 2" diameter        Coal Capacity 1 ton
Heating Surface 1132 sq.ft. total            Length over buffers 29' 0 1/2"
Grate area 15 3/4 sq.ft.                         Weight (in working order) 43 tons 6 cwt.
Working Pressure 140 p.s.i.

Consent Iron Company became far and away the last to buy the type and they had a series built at intervals, from 1872; the last three were delivered as late as 1941.