Maunsell was succeeded in 1937 by Oliver Vaughan Snell Bulleid, who brought experience gained under Sir Nigel Gresley at the LNER. He designed the Bulleid chain-driven valve gear that was compact enough to fit within the restrictions of his "Pacific" designs, the Merchant Navy class of 1941 and the "Light Pacific" design of 1945. Ever the innovator, Bulleid introduced welded steel boilers and steel fireboxes which were easier to repair than the copper variety, whilst a new emphasis on cab ergonomics was followed. Established locomotive design practices were altered in his designs, with the wheels changed from the traditional spoked to his BFB disc wheel design, giving better all-round support to the tyre.