Like the two forerunners , they were excellent steamers and , with the improvements , gave a much better performance .
Built by NBL , it was an improved version of the predecessor Class 4 , with a superheater and Walschaerts valve gear .
Like the two forerunners , NBL were excellent steamers and , with the improvements , gave a much better performance .
Built by NBL , it was an improved version of the predecessor Class 4 , with a superheater and Walschaerts valve gear .