The Great Eastern class L77 was a 0-6-2T tank locomotive with drivers of 58 inches (1,473 mm) for suburban services around London. For this task they had Westinghouse air brakes and some were also equipped with a condenser. Other features were inside cylinders, inside Walschaerts valve gear and a Belpaire firebox. 

Only the first two were built at Stratford in 1915, with 20 more being ordered by the GER. Ten of these were delivered in 1921 and the other ten were directly delivered to the LNER in 1923 and 1924. There they were designated class N7 and between 1925 and 1928, 110 more were delivered by the LNER works at Gorton and Doncaster and by Robert Stephenson & Co. and William Beardmore & Co.

Different variants built and rebuilt under Gresley led to the sub classes N7/1 to N7/5. All later received new boilers with round-topped fireboxes. Most were withdrawn by British Railways between 1959 and 1961, with the last nine disappearing in 1962. Today only 69621, ex LNER 7999, is preserved. It is being owned by the East Anglian Railway Museum and not in working order.