In 1863 the Great Northern Railway were suddenly called upon to provide locomotive power for the working of their trains through the portion of the Metropolitan Railway over which they possessed running powers, and this necessity being unexpectedly brought forward, found the company in some difficulty, as at the time they had no tank engines which were specially fitted for the purpose. There were, however, a certain number of the “Little Sharps” which had already been converted into passenger tank locomotives by Mr. Sturrock, in 1852-3, which were utilized as makeshifts pending the provision of engines suitable for “underground” traffic.
These new engines were specially designed by Mr. Sturrock for the working of underground traffic, and were built in 1865 by the Avonside Engine Co., of Bristol (makers’ Nos. 607 to 616). They bore the G.N.R. Nos. 241 to 250, and were of the type shown in the accompanying illustration. Fig. 27, of No. 241, having four-coupled wheels in front, a single pair of trailing wheels with radial axleboxes at the rear, and a large tank and coal bunker directly over the trailing wheels. Condensing was provided for by means of a long pipe running below the footplate into the tank.
The leading dimensions of the engines were : diameter of coupled wheels 5-ft. 6-in., and of trailing wheels 4-ft.; wheel-base: leading to driving wheel centres 7-ft. 6-in., driving to trailing wheel centres 11-ft. 9-in., total 19-ft. 3-in.; cylinders 16 1/2-in. by 22-in.; boiler barrel, length 10-ft., diameter 4-ft.; length of firebox casing 4-ft. 6-in.; total heating surface 867-1 sq. ft.; total weight in working order, 39 tons 12 cwt. 2 qrs.
So successful did the engines last mentioned prove that others to the number of ten were supplied in 1866, Nos. 270 to 274 by Messrs. Neilson & Co., of Glasgow (makers’ Nos. 131 1 to 1315), and Nos. 275 to 279 by the Avonside Engine Co. Those built by Messrs. Neilson had a 12 -in. longer wheel-base, and weighed about 30 cwt. more than the first lot put on the rails, and were of the general design shown in the accompanying illustration of No. 270, Fig. 28.