Complex sentence: The D class was a Harry Wainwright design and was responsible for the the overall look of the engine the detail work was undertaken by Robert Surtees, his chief draughtsman at Ashford works.
Split into simpler sentences: The D class was a Harry Wainwright design and he was responsible for the the overall look of the engine. The detail work was undertaken by Robert Surtees, his chief draughtsman at Ashford works.